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 Number System 
 Basics of Number System 
 (1).  Face  Value  :  It  is  nothing  but  the 
 number  itself  about  which  it  has  been 
 asked. 
 Eg:  In  the  number  23576,  face  value  of  5 
 is 5 and face value of 7 is 7. 
 (2).  Place  Value  :  The  place  value  of  a 
 number  depends  on  its  position  in  the 
 number.  Each  position  has  a  value  10 
 n 
 , 
 the places to its right. 
 Eg:  In  the  number  23576,  place  value  of  5 
 is 500 and place value of 3 is 3000. 
 Types of Numbers 
 (1). Natural Numbers (N) : 
 All  positive  counting  numbers.  (0  is  not 
 included in it.) 
 Examples: 1, 2, 3, 4 … etc. 
 (2).  Whole  Numbers  (W):  All  non- 
 negative numbers are all whole numbers. 
 Examples: 0, 1, 2, 3, 4… etc. 
 (3).  Integer  Numbers  (I):  All  positive 
 numbers  and  negative  numbers 
 including  zero.  Positive  numbers  are 
 called  positive  integers  and  negative 
 numbers are called negative integers. 
 I = ….. , -4, - 3, - 2, - 1, 0, 1, 2, 3, 4 …... 
 (4).  Even  Numbers  :  2,  4,  6,  8,  10….. 
 [Divisible by 2 completely] 
 (5).  Odd  Numbers  :  1,  3,  5,  7,  9,  11…..  [Not 
 divisible by 2 completely] 
 (6).  Rational  Numbers  :  Numbers  whose 
 exact  value  can  be  determined.  Also  a 
 number  which  can  be  written  in  the  form 
 ,  where  p  and  q  are  integers  and  q  ?  0
 ?? 
 ?? 
 is called a rational  number. For example, 
 Examples :  = 0.75,  = 0.8  ,  , 
 3 
 4 
 4 
 5 
 9 
- 5 
 22 
 7
 (7).  Irrational  Numbers  :  Numbers  whose 
 exact value cannot be determined. 
 Example :  = 3.142857142857 … p
 (8).  Prime  number  :  A  number  which  is 
 divisible  by  1  and  itself.  2  is  only  an  even 
 prime number. 
 Example : 2, 3, 5, 7, 11, etc. 
 Note:- 
 Total prime no. between 1 - 50  15 ?
 Total prime no. between 1 - 100  25 ?
 Total prime no. between 1 - 500  95 ?
 Total prime no. between 1 - 1000  168 ?
 (9).  Composite  number  :  If  we  remove  all 
 prime  numbers  from  natural  numbers 
 then whatever is left is called Composite 
 numbers. 
 Example : 4, 6, 8, 9, 10, 12 etc. 
 Note :-  1 is neither prime nor composite. 
 (10).  Co  -  prime  number  :  Two  numbers 
 are  called  Co-prime  numbers  if  their  HCF 
 is 1. 
 Example  : (2 and 3), (6 and 11). 
 Note  :  Two  prime  numbers  are  always 
 co-prime  numbers  to  each  other.  Any  two 
 consecutive  integers  are  always  co-prime 
 number to each other. 
 Factors 
 The  factors  of  a  number  are  the  numbers 
 that  divide  it  completely  without  leaving 
 any remainder. 
 Example  :  24  can  be  completely  divided 
 by  1,  2,  3,  4,  6,  8,  12  and  24,  so  these 
 numbers are factors of 24. 
 Prime  factorisation  of  a  number  :  When 
 a  number  is  written  in  the  form  of 
 multiplication  of  its  prime  factors,  it's 
 called prime factorisation. 
 Prime factorisation of 24. 
 24  2  2  2  3 or ?   ×      ×   ×    2 
 3 
×    3 
 1
 Number  of  factors  :  To  ?nd  the  number 
 of  factors  we  write  the  number  in  the 
 form  of  prime  factors  and  then  add  +1  to 
 the  exponent  of  prime  factors  and 
 multiply them. 
 For example: 24 =  2 
 3 
×    3 
 1
 Number  of  factors  of  24  (3  +  1)(1  +  1) ?
 = 4  2 = 8. ×
 With  the  help  of  an  example,  we  try  to 
 ?nd the sum of all factors of a number. 
 24 =  ,  2 
 3 
× 3 
 1
 Sum  of  all  factors  =  (  +  )  2 
 0 
+ 2 
 1 
 2 
 2 
+ 2 
 3 
×
 (  ) = 15  4 = 60.  3 
 0 
+ 3 
 1 
×
 Number  of  even  factors  of  a  number  :  To 
 ?nd  the  number  of  even  factors  of  a 
 number,  we  add  +1  to  the  exponents  of 
 prime numbers except 2. 
 (Note  :  If  a  number  doesn't  have  2  as  its 
 factor it will have 0 even factors) 
 Que  .  Find  the  number  of  even  factors  of 
 120. 
 Ans. 120 =  2 
 3 
× 3 
 1 
× 5 
 1
 Number  of  even  factors  =  3  (1  +  1) × ×
 (1 + 1) = 3  2  2 = 12 × ×
 Note :-  To ?nd  the sum of even factors  , 
 we shall ignore  ,  2 
 0 
 Que.  Find the sum of even factors of 120. 
 Sol:-  Sum of even factors = (  + +  )  2 
 1 
    2 
 2 
 2 
 3 
 (  )(  ) = 14  4  6 = 336.  3 
 0 
+ 3 
 1 
 5 
 0 
+    5 
 1 
   ×   ×   
 Number  and  Sum  of  odd  factors  of  a 
 number  :  to  ?nd  the  number  and  sum  of 
 odd  factors  of  a  number,  we  have  to 
 ignore the exponents of 2. 
 Que  . Find the number of odd factors 120. 
 Sol:-  120 =  2 
 3 
× 3 
 1 
× 5 
 1
 Required number = (1 + 1)(1 + 1) = 4 
 The exponent of 2 is completely ignored. 
 Sum  of  odd  factors  of  120  =  (  )(  3 
 0 
+  3 
 1 
 ) = 4  6 = 24  5 
 0 
+ 5 
 1 
   ×
 Some Important Results of Factors: 
 1001 = 7  11  13 ×   ×
 1001  abc = abcabc ×
 1001  234 = 234234 ×
 Que:  Which  of  the  following  is  a  factor  of 
 531531? 
 (a) 15   (b) 13   (c) 11   (d) both b and c
 Sol:-  531531 = 1001  531 ×
 =  7  11  13  531  So,  both  11  and  13 × × ×
 are factors of 531531. 
 111 = 37  3 , 1001  111 = 111111, × ×
 When  a  single  digit  is  written  6  times,  3, 
 7, 11, 13, and 37 are factors of it. 
 Que  .  Which  of  the  following  is  a  factor  of 
 222222 ? 
 (a) 17  (b) 57     (c) 68  (d) 74
 Sol  :- 222222 = 2  111111    ×
 = 2  37 × 3 × 7 ×    11 × 13    ×
 Clearly, 2  37 = 74 is one of the factors. ×
 ? If a, b and c are prime numbers, then
 the number of prime factors of  ?? 
 ?? 
×    ?? 
 ?? 
×
 is (x + y + z).  ?? 
 ?? 
 Recurring Decimal 
 Recurring  decimals  are  referred  to  as 
 numbers  that  are  uniformly  repeated 
 after  the  decimal.  Some  rational 
 numbers  produce  recurring  decimals 
 after  converting  them  into  decimal 
 numbers,  but  all  irrational  numbers 
 produce  recurring  decimals  after 
 converting them into decimal form. 
 Examples : 
 (1)  = 0.3333333 ….. = 0. 
 1 
 3 
 3
 (2) 0.  =  = 1 9 
 9 
 9 
 (3) 0.53  = =  27 
 5327    -    53 
 9900 
 5274 
 9900 
  
Page 2


      
 Number System 
 Basics of Number System 
 (1).  Face  Value  :  It  is  nothing  but  the 
 number  itself  about  which  it  has  been 
 asked. 
 Eg:  In  the  number  23576,  face  value  of  5 
 is 5 and face value of 7 is 7. 
 (2).  Place  Value  :  The  place  value  of  a 
 number  depends  on  its  position  in  the 
 number.  Each  position  has  a  value  10 
 n 
 , 
 the places to its right. 
 Eg:  In  the  number  23576,  place  value  of  5 
 is 500 and place value of 3 is 3000. 
 Types of Numbers 
 (1). Natural Numbers (N) : 
 All  positive  counting  numbers.  (0  is  not 
 included in it.) 
 Examples: 1, 2, 3, 4 … etc. 
 (2).  Whole  Numbers  (W):  All  non- 
 negative numbers are all whole numbers. 
 Examples: 0, 1, 2, 3, 4… etc. 
 (3).  Integer  Numbers  (I):  All  positive 
 numbers  and  negative  numbers 
 including  zero.  Positive  numbers  are 
 called  positive  integers  and  negative 
 numbers are called negative integers. 
 I = ….. , -4, - 3, - 2, - 1, 0, 1, 2, 3, 4 …... 
 (4).  Even  Numbers  :  2,  4,  6,  8,  10….. 
 [Divisible by 2 completely] 
 (5).  Odd  Numbers  :  1,  3,  5,  7,  9,  11…..  [Not 
 divisible by 2 completely] 
 (6).  Rational  Numbers  :  Numbers  whose 
 exact  value  can  be  determined.  Also  a 
 number  which  can  be  written  in  the  form 
 ,  where  p  and  q  are  integers  and  q  ?  0
 ?? 
 ?? 
 is called a rational  number. For example, 
 Examples :  = 0.75,  = 0.8  ,  , 
 3 
 4 
 4 
 5 
 9 
- 5 
 22 
 7
 (7).  Irrational  Numbers  :  Numbers  whose 
 exact value cannot be determined. 
 Example :  = 3.142857142857 … p
 (8).  Prime  number  :  A  number  which  is 
 divisible  by  1  and  itself.  2  is  only  an  even 
 prime number. 
 Example : 2, 3, 5, 7, 11, etc. 
 Note:- 
 Total prime no. between 1 - 50  15 ?
 Total prime no. between 1 - 100  25 ?
 Total prime no. between 1 - 500  95 ?
 Total prime no. between 1 - 1000  168 ?
 (9).  Composite  number  :  If  we  remove  all 
 prime  numbers  from  natural  numbers 
 then whatever is left is called Composite 
 numbers. 
 Example : 4, 6, 8, 9, 10, 12 etc. 
 Note :-  1 is neither prime nor composite. 
 (10).  Co  -  prime  number  :  Two  numbers 
 are  called  Co-prime  numbers  if  their  HCF 
 is 1. 
 Example  : (2 and 3), (6 and 11). 
 Note  :  Two  prime  numbers  are  always 
 co-prime  numbers  to  each  other.  Any  two 
 consecutive  integers  are  always  co-prime 
 number to each other. 
 Factors 
 The  factors  of  a  number  are  the  numbers 
 that  divide  it  completely  without  leaving 
 any remainder. 
 Example  :  24  can  be  completely  divided 
 by  1,  2,  3,  4,  6,  8,  12  and  24,  so  these 
 numbers are factors of 24. 
 Prime  factorisation  of  a  number  :  When 
 a  number  is  written  in  the  form  of 
 multiplication  of  its  prime  factors,  it's 
 called prime factorisation. 
 Prime factorisation of 24. 
 24  2  2  2  3 or ?   ×      ×   ×    2 
 3 
×    3 
 1
 Number  of  factors  :  To  ?nd  the  number 
 of  factors  we  write  the  number  in  the 
 form  of  prime  factors  and  then  add  +1  to 
 the  exponent  of  prime  factors  and 
 multiply them. 
 For example: 24 =  2 
 3 
×    3 
 1
 Number  of  factors  of  24  (3  +  1)(1  +  1) ?
 = 4  2 = 8. ×
 With  the  help  of  an  example,  we  try  to 
 ?nd the sum of all factors of a number. 
 24 =  ,  2 
 3 
× 3 
 1
 Sum  of  all  factors  =  (  +  )  2 
 0 
+ 2 
 1 
 2 
 2 
+ 2 
 3 
×
 (  ) = 15  4 = 60.  3 
 0 
+ 3 
 1 
×
 Number  of  even  factors  of  a  number  :  To 
 ?nd  the  number  of  even  factors  of  a 
 number,  we  add  +1  to  the  exponents  of 
 prime numbers except 2. 
 (Note  :  If  a  number  doesn't  have  2  as  its 
 factor it will have 0 even factors) 
 Que  .  Find  the  number  of  even  factors  of 
 120. 
 Ans. 120 =  2 
 3 
× 3 
 1 
× 5 
 1
 Number  of  even  factors  =  3  (1  +  1) × ×
 (1 + 1) = 3  2  2 = 12 × ×
 Note :-  To ?nd  the sum of even factors  , 
 we shall ignore  ,  2 
 0 
 Que.  Find the sum of even factors of 120. 
 Sol:-  Sum of even factors = (  + +  )  2 
 1 
    2 
 2 
 2 
 3 
 (  )(  ) = 14  4  6 = 336.  3 
 0 
+ 3 
 1 
 5 
 0 
+    5 
 1 
   ×   ×   
 Number  and  Sum  of  odd  factors  of  a 
 number  :  to  ?nd  the  number  and  sum  of 
 odd  factors  of  a  number,  we  have  to 
 ignore the exponents of 2. 
 Que  . Find the number of odd factors 120. 
 Sol:-  120 =  2 
 3 
× 3 
 1 
× 5 
 1
 Required number = (1 + 1)(1 + 1) = 4 
 The exponent of 2 is completely ignored. 
 Sum  of  odd  factors  of  120  =  (  )(  3 
 0 
+  3 
 1 
 ) = 4  6 = 24  5 
 0 
+ 5 
 1 
   ×
 Some Important Results of Factors: 
 1001 = 7  11  13 ×   ×
 1001  abc = abcabc ×
 1001  234 = 234234 ×
 Que:  Which  of  the  following  is  a  factor  of 
 531531? 
 (a) 15   (b) 13   (c) 11   (d) both b and c
 Sol:-  531531 = 1001  531 ×
 =  7  11  13  531  So,  both  11  and  13 × × ×
 are factors of 531531. 
 111 = 37  3 , 1001  111 = 111111, × ×
 When  a  single  digit  is  written  6  times,  3, 
 7, 11, 13, and 37 are factors of it. 
 Que  .  Which  of  the  following  is  a  factor  of 
 222222 ? 
 (a) 17  (b) 57     (c) 68  (d) 74
 Sol  :- 222222 = 2  111111    ×
 = 2  37 × 3 × 7 ×    11 × 13    ×
 Clearly, 2  37 = 74 is one of the factors. ×
 ? If a, b and c are prime numbers, then
 the number of prime factors of  ?? 
 ?? 
×    ?? 
 ?? 
×
 is (x + y + z).  ?? 
 ?? 
 Recurring Decimal 
 Recurring  decimals  are  referred  to  as 
 numbers  that  are  uniformly  repeated 
 after  the  decimal.  Some  rational 
 numbers  produce  recurring  decimals 
 after  converting  them  into  decimal 
 numbers,  but  all  irrational  numbers 
 produce  recurring  decimals  after 
 converting them into decimal form. 
 Examples : 
 (1)  = 0.3333333 ….. = 0. 
 1 
 3 
 3
 (2) 0.  =  = 1 9 
 9 
 9 
 (3) 0.53  = =  27 
 5327    -    53 
 9900 
 5274 
 9900 
  
      
 (4) 2.53  = 2 +  = 2  27 
 5327    -    53 
 9900 
 5274 
 9900 
 Divisibility Test 
 By  2:-  When  last  digit  is  0  or  an  even 
 number     eg: 520, 588 
 By 3:-  Sum of digits is divisible by 3 
 eg: 1971, 1974 
 By  4:-  When  last  two  digits  are  divisible 
 by 4 or, they are zeros eg: 1528, 1700 
 By 5 :-  When last digit is 0 or 5 
 eg: 1725, 1790 
 By  6  :-  When  the  number  is  divisible  by  2 
 and 3 both. eg: 36, 72 
 By  7  :  -  Subtract  twice  the  last  digit  from 
 the  number  formed  by  the  remaining 
 digits. Like  651 divisible by 7 
 65  -  (1  ×  2)  =  63.  Since  63  is  divisible  by 
 7, so is 651. 
 By  8  :-  When  the  last  three  digits  are 
 divisible by 8.  eg: 2256 
 By  9  :-  When  sum  of  digit  is  divisible  by  9 
 eg: 9216 
 By  10  :-  When  the  last  digit  is  0.  eg: 
 452600 
 By  11:-  When  the  difference  between  the 
 sum  of  odd  and  even  place  digits  is 
 equal to 0 or multiple of 11 . 
 eg: 217382 
 Sum of odd place digits = 2 + 7 + 8 = 17 
 Sum of even place digits = 1 + 3 + 2 = 6 
 17 – 6 = 11, hence 217382 is divisible by 
 11. 
 By  13  :  -  If  adding  four  times  the  last 
 digit  to  the  number  formed  by  the 
 remaining  digits  is  divisible  by  13,  then 
 the  number  is  divisible  by  13.  Like  1326 
 is divisible by 13 
 132  +  (6  4)  =  156.  Repeat  the  same  × 
 process for 156 . 
 15 + (6  4) = 39.so 39 is divisible by 13  × 
 BY  17  :-  The  divisibility  rule  of  17  states, 
 "If  ?ve  times  the  last  digit  is  subtracted 
 from  a  number  made  up  of  the  remaining 
 digits  and  the  remainder  is  either  0  or  a 
 multiple  of  17,  then  the  number  is 
 divisible by 17". 
 Like 221: 22 - 1 × 5 = 17. 
 Prime Number Test 
 For  ?nding  whether  any  number  is  a 
 prime  number  or  not,  we  need  to  ?nd  the 
 nearest  square  root  of  given  number, 
 then  we  need  to  ?nd  out  whether  the 
 given  number  is  divisible  by  any  prime 
 number  less  than  the  obtained  number  or 
 not.  If  it  is  divisible  then  it  is  not  a  prime 
 number and if not divisible then it is a 
 prime number. 
 Example  :  Find  whether  177  is  a  prime 
 number or not. 
 Soln  :  Nearest  square  root  of  177  is  13. 
 Now  we  need  to  check  whether  177  is 
 divisible  by  prime  numbers  less  than  13. 
 On  checking  we  ?nd  that  177  is  divisible 
 by 3. Hence, 177 is not a prime number. 
 Important Formulas 
 1.  Sum of ?rst n natural number 
 s = 
 ?? ( ??    +    1 )
 2 
 2.  Sum of ?rst n odd numbers =  ?? 
 2 
 3.  Sum of ?rst n even numbers 
 =  ?? ( ?? + 1 )
 4.  Sum  of  square  of  ?rst  n  natural 
 numbers = 
 ?? ( ??    +    1 )( 2  ??    +    1 )
 6 
 5.  Sum  of  cubes  of  ?rst  n  natural 
 number = (  ) 
 2 
 ?? ( ??    +    1 )
 2 
 6.  is  divisible  by  for ( ?? 
 ?? 
- ?? 
 ?? 
) ?? - ?? ( )   
 every natural number m. 
 7.  is  divisible  by  and ( ?? 
 ?? 
- ?? 
 ?? 
) ?? + ?? ( )   
 for even values of m.  ?? - ?? ( )
 8.  is  divisible  by  for ( ?? 
 ?? 
+ ?? 
 ?? 
) ?? + ?? ( )   
 odd values of m. 
 9.  Number  of  prime  factors  of 
 is  when  a,  ?? 
 ?? 
,    ?? 
 ?? 
,    ?? 
 ?? 
,    ??    
 ?? 
    ?? + ?? + ?? + ?? 
 b, c, d are all prime numbers. 
 10.  HCF of  and  = ( ?? 
 ?? 
- 1 ) ( ?? 
 ?? 
- 1 )
 [  ] ( ?? 
 ?????? ( ?? ,    ?? )
- 1 )
 Number of Zeros in an expression 
 We  shall  understand  this  concept  with 
 the help of an example. 
 Let’s  ?nd  the  number  of  zeros  in  the 
 following  expression:  24  32  17  23 × × ×
 19 = (2 
 3 
 × 3 
 1 
 )  2 
 5 
 × 17 × 23 × 19 × × 
 Notice  that  a  zero  is  made  only  when 
 there  is  a  combination  of  2  and  5.  Since 
 there  is  no  ‘5’  here  there  will  be  no  zero  in 
 the above expression. 
 Example:- 
 8     ×     15     ×     23     ×     17     ×     25     ×     22 =
 2 
 3 
× ( 3 
 1 
× 5 
 1 
)    ×     23     ×     17     ×     5 
 2 
×    2 
 1 
    ×     11 
 In  this  expression  there  are  4  twos  and  3 
 ?ves.  From  this  3  pairs  of  can  be  5×2 
 formed.  Therefore,  there  will  be  3  zeros 
 in the ?nal product. 
 Que  .  Find  the  number  of  zeros  in  the 
 value of: 
 2 
 2 
× 5 
 4 
× 4 
 6 
× 10 
 8 
× 6 
 10 
× 15 
 12 
× 8 
 14 
 . × 20 
 16 
× 10 
 18 
× 25 
 20 
 Sol:- 
 2 
 2 
× 5 
 4 
× 4 
 6 
× 10 
 8 
× 6 
 10 
× 15 
 12 
× 8 
 14 
 = × 20 
 16 
× 10 
 18 
× 25 
 20 
 2 
 2 
× 5 
 4 
× 2 
 12 
× 2 
 8 
× 5 
 8 
× 2 
 10 
× 3 
 10 
× 3 
 12 
× 5 
 12 
× 2 
 42 
× 2 
 32 
× 5 
 16 
× 2 
 18 
× 5 
 18 
× 5 
 40 
 Zeros  are  possible  with  a  combination  of 
 2  Here  the  number  of  5’s  are  less  so     ×     5 
 the  number  of  zeros  will  be  limited  to  the 
 number of 5’s. 
 In  this  expression  number  of  ?ves  are: 
 5 
 4 
× 5 
 8 
× 5 
 12 
× 5 
 16 
× 5 
 18 
× 5 
 40 
;
 i.e. 4 + 8 + 12 + 16 + 18 + 40 = 98 
 The number of Zeros in n! 
 To  ?nd  the  number  of  zeros  in  n!,  we 
 divide  “n”  by  5  until  we  get  a  number  less 
 than  5,  and  then  we  add  all  the  quotients 
 so obtained. 
 Que.  Find the number of zeros in 36! . 
 The number of zeros = 7 + 1 = 8. 
 Remainder Theorem 
 Que.  What  will  be  the  remainder  when 
 is divided by 12?  17     ×     23 
 Ans :-  We can express this as: 
 =  17     ×     23  12 + 5 ( ) × 12 + 11 ( )
= 12     ×     12 + 12     ×     11 + 5     ×     12 + 5  ×  11 
 In  the  above  expression  we  will  ?nd  that 
 remainder  will  depend  on  the  last  term 
 i.e.  5     ×     11 
 Now,  .(  )  7.  ?????? 
 5     ×     11 
 12 
=
 So, 
 12     ×     12    +    12        ×     11    +    5     ×     12    +    5     ×     11 
 12 
 and  remainder  is  same  in  both 
 5     ×     11 
 12 
 cases which is 7. 
 Example:-  Remainder when 
 is divided by 12?  1421     ×     1423     ×     1425 
 (  )  ?????? 
 1421     ×     1423     ×     1425 
 12 
  
Page 3


      
 Number System 
 Basics of Number System 
 (1).  Face  Value  :  It  is  nothing  but  the 
 number  itself  about  which  it  has  been 
 asked. 
 Eg:  In  the  number  23576,  face  value  of  5 
 is 5 and face value of 7 is 7. 
 (2).  Place  Value  :  The  place  value  of  a 
 number  depends  on  its  position  in  the 
 number.  Each  position  has  a  value  10 
 n 
 , 
 the places to its right. 
 Eg:  In  the  number  23576,  place  value  of  5 
 is 500 and place value of 3 is 3000. 
 Types of Numbers 
 (1). Natural Numbers (N) : 
 All  positive  counting  numbers.  (0  is  not 
 included in it.) 
 Examples: 1, 2, 3, 4 … etc. 
 (2).  Whole  Numbers  (W):  All  non- 
 negative numbers are all whole numbers. 
 Examples: 0, 1, 2, 3, 4… etc. 
 (3).  Integer  Numbers  (I):  All  positive 
 numbers  and  negative  numbers 
 including  zero.  Positive  numbers  are 
 called  positive  integers  and  negative 
 numbers are called negative integers. 
 I = ….. , -4, - 3, - 2, - 1, 0, 1, 2, 3, 4 …... 
 (4).  Even  Numbers  :  2,  4,  6,  8,  10….. 
 [Divisible by 2 completely] 
 (5).  Odd  Numbers  :  1,  3,  5,  7,  9,  11…..  [Not 
 divisible by 2 completely] 
 (6).  Rational  Numbers  :  Numbers  whose 
 exact  value  can  be  determined.  Also  a 
 number  which  can  be  written  in  the  form 
 ,  where  p  and  q  are  integers  and  q  ?  0
 ?? 
 ?? 
 is called a rational  number. For example, 
 Examples :  = 0.75,  = 0.8  ,  , 
 3 
 4 
 4 
 5 
 9 
- 5 
 22 
 7
 (7).  Irrational  Numbers  :  Numbers  whose 
 exact value cannot be determined. 
 Example :  = 3.142857142857 … p
 (8).  Prime  number  :  A  number  which  is 
 divisible  by  1  and  itself.  2  is  only  an  even 
 prime number. 
 Example : 2, 3, 5, 7, 11, etc. 
 Note:- 
 Total prime no. between 1 - 50  15 ?
 Total prime no. between 1 - 100  25 ?
 Total prime no. between 1 - 500  95 ?
 Total prime no. between 1 - 1000  168 ?
 (9).  Composite  number  :  If  we  remove  all 
 prime  numbers  from  natural  numbers 
 then whatever is left is called Composite 
 numbers. 
 Example : 4, 6, 8, 9, 10, 12 etc. 
 Note :-  1 is neither prime nor composite. 
 (10).  Co  -  prime  number  :  Two  numbers 
 are  called  Co-prime  numbers  if  their  HCF 
 is 1. 
 Example  : (2 and 3), (6 and 11). 
 Note  :  Two  prime  numbers  are  always 
 co-prime  numbers  to  each  other.  Any  two 
 consecutive  integers  are  always  co-prime 
 number to each other. 
 Factors 
 The  factors  of  a  number  are  the  numbers 
 that  divide  it  completely  without  leaving 
 any remainder. 
 Example  :  24  can  be  completely  divided 
 by  1,  2,  3,  4,  6,  8,  12  and  24,  so  these 
 numbers are factors of 24. 
 Prime  factorisation  of  a  number  :  When 
 a  number  is  written  in  the  form  of 
 multiplication  of  its  prime  factors,  it's 
 called prime factorisation. 
 Prime factorisation of 24. 
 24  2  2  2  3 or ?   ×      ×   ×    2 
 3 
×    3 
 1
 Number  of  factors  :  To  ?nd  the  number 
 of  factors  we  write  the  number  in  the 
 form  of  prime  factors  and  then  add  +1  to 
 the  exponent  of  prime  factors  and 
 multiply them. 
 For example: 24 =  2 
 3 
×    3 
 1
 Number  of  factors  of  24  (3  +  1)(1  +  1) ?
 = 4  2 = 8. ×
 With  the  help  of  an  example,  we  try  to 
 ?nd the sum of all factors of a number. 
 24 =  ,  2 
 3 
× 3 
 1
 Sum  of  all  factors  =  (  +  )  2 
 0 
+ 2 
 1 
 2 
 2 
+ 2 
 3 
×
 (  ) = 15  4 = 60.  3 
 0 
+ 3 
 1 
×
 Number  of  even  factors  of  a  number  :  To 
 ?nd  the  number  of  even  factors  of  a 
 number,  we  add  +1  to  the  exponents  of 
 prime numbers except 2. 
 (Note  :  If  a  number  doesn't  have  2  as  its 
 factor it will have 0 even factors) 
 Que  .  Find  the  number  of  even  factors  of 
 120. 
 Ans. 120 =  2 
 3 
× 3 
 1 
× 5 
 1
 Number  of  even  factors  =  3  (1  +  1) × ×
 (1 + 1) = 3  2  2 = 12 × ×
 Note :-  To ?nd  the sum of even factors  , 
 we shall ignore  ,  2 
 0 
 Que.  Find the sum of even factors of 120. 
 Sol:-  Sum of even factors = (  + +  )  2 
 1 
    2 
 2 
 2 
 3 
 (  )(  ) = 14  4  6 = 336.  3 
 0 
+ 3 
 1 
 5 
 0 
+    5 
 1 
   ×   ×   
 Number  and  Sum  of  odd  factors  of  a 
 number  :  to  ?nd  the  number  and  sum  of 
 odd  factors  of  a  number,  we  have  to 
 ignore the exponents of 2. 
 Que  . Find the number of odd factors 120. 
 Sol:-  120 =  2 
 3 
× 3 
 1 
× 5 
 1
 Required number = (1 + 1)(1 + 1) = 4 
 The exponent of 2 is completely ignored. 
 Sum  of  odd  factors  of  120  =  (  )(  3 
 0 
+  3 
 1 
 ) = 4  6 = 24  5 
 0 
+ 5 
 1 
   ×
 Some Important Results of Factors: 
 1001 = 7  11  13 ×   ×
 1001  abc = abcabc ×
 1001  234 = 234234 ×
 Que:  Which  of  the  following  is  a  factor  of 
 531531? 
 (a) 15   (b) 13   (c) 11   (d) both b and c
 Sol:-  531531 = 1001  531 ×
 =  7  11  13  531  So,  both  11  and  13 × × ×
 are factors of 531531. 
 111 = 37  3 , 1001  111 = 111111, × ×
 When  a  single  digit  is  written  6  times,  3, 
 7, 11, 13, and 37 are factors of it. 
 Que  .  Which  of  the  following  is  a  factor  of 
 222222 ? 
 (a) 17  (b) 57     (c) 68  (d) 74
 Sol  :- 222222 = 2  111111    ×
 = 2  37 × 3 × 7 ×    11 × 13    ×
 Clearly, 2  37 = 74 is one of the factors. ×
 ? If a, b and c are prime numbers, then
 the number of prime factors of  ?? 
 ?? 
×    ?? 
 ?? 
×
 is (x + y + z).  ?? 
 ?? 
 Recurring Decimal 
 Recurring  decimals  are  referred  to  as 
 numbers  that  are  uniformly  repeated 
 after  the  decimal.  Some  rational 
 numbers  produce  recurring  decimals 
 after  converting  them  into  decimal 
 numbers,  but  all  irrational  numbers 
 produce  recurring  decimals  after 
 converting them into decimal form. 
 Examples : 
 (1)  = 0.3333333 ….. = 0. 
 1 
 3 
 3
 (2) 0.  =  = 1 9 
 9 
 9 
 (3) 0.53  = =  27 
 5327    -    53 
 9900 
 5274 
 9900 
  
      
 (4) 2.53  = 2 +  = 2  27 
 5327    -    53 
 9900 
 5274 
 9900 
 Divisibility Test 
 By  2:-  When  last  digit  is  0  or  an  even 
 number     eg: 520, 588 
 By 3:-  Sum of digits is divisible by 3 
 eg: 1971, 1974 
 By  4:-  When  last  two  digits  are  divisible 
 by 4 or, they are zeros eg: 1528, 1700 
 By 5 :-  When last digit is 0 or 5 
 eg: 1725, 1790 
 By  6  :-  When  the  number  is  divisible  by  2 
 and 3 both. eg: 36, 72 
 By  7  :  -  Subtract  twice  the  last  digit  from 
 the  number  formed  by  the  remaining 
 digits. Like  651 divisible by 7 
 65  -  (1  ×  2)  =  63.  Since  63  is  divisible  by 
 7, so is 651. 
 By  8  :-  When  the  last  three  digits  are 
 divisible by 8.  eg: 2256 
 By  9  :-  When  sum  of  digit  is  divisible  by  9 
 eg: 9216 
 By  10  :-  When  the  last  digit  is  0.  eg: 
 452600 
 By  11:-  When  the  difference  between  the 
 sum  of  odd  and  even  place  digits  is 
 equal to 0 or multiple of 11 . 
 eg: 217382 
 Sum of odd place digits = 2 + 7 + 8 = 17 
 Sum of even place digits = 1 + 3 + 2 = 6 
 17 – 6 = 11, hence 217382 is divisible by 
 11. 
 By  13  :  -  If  adding  four  times  the  last 
 digit  to  the  number  formed  by  the 
 remaining  digits  is  divisible  by  13,  then 
 the  number  is  divisible  by  13.  Like  1326 
 is divisible by 13 
 132  +  (6  4)  =  156.  Repeat  the  same  × 
 process for 156 . 
 15 + (6  4) = 39.so 39 is divisible by 13  × 
 BY  17  :-  The  divisibility  rule  of  17  states, 
 "If  ?ve  times  the  last  digit  is  subtracted 
 from  a  number  made  up  of  the  remaining 
 digits  and  the  remainder  is  either  0  or  a 
 multiple  of  17,  then  the  number  is 
 divisible by 17". 
 Like 221: 22 - 1 × 5 = 17. 
 Prime Number Test 
 For  ?nding  whether  any  number  is  a 
 prime  number  or  not,  we  need  to  ?nd  the 
 nearest  square  root  of  given  number, 
 then  we  need  to  ?nd  out  whether  the 
 given  number  is  divisible  by  any  prime 
 number  less  than  the  obtained  number  or 
 not.  If  it  is  divisible  then  it  is  not  a  prime 
 number and if not divisible then it is a 
 prime number. 
 Example  :  Find  whether  177  is  a  prime 
 number or not. 
 Soln  :  Nearest  square  root  of  177  is  13. 
 Now  we  need  to  check  whether  177  is 
 divisible  by  prime  numbers  less  than  13. 
 On  checking  we  ?nd  that  177  is  divisible 
 by 3. Hence, 177 is not a prime number. 
 Important Formulas 
 1.  Sum of ?rst n natural number 
 s = 
 ?? ( ??    +    1 )
 2 
 2.  Sum of ?rst n odd numbers =  ?? 
 2 
 3.  Sum of ?rst n even numbers 
 =  ?? ( ?? + 1 )
 4.  Sum  of  square  of  ?rst  n  natural 
 numbers = 
 ?? ( ??    +    1 )( 2  ??    +    1 )
 6 
 5.  Sum  of  cubes  of  ?rst  n  natural 
 number = (  ) 
 2 
 ?? ( ??    +    1 )
 2 
 6.  is  divisible  by  for ( ?? 
 ?? 
- ?? 
 ?? 
) ?? - ?? ( )   
 every natural number m. 
 7.  is  divisible  by  and ( ?? 
 ?? 
- ?? 
 ?? 
) ?? + ?? ( )   
 for even values of m.  ?? - ?? ( )
 8.  is  divisible  by  for ( ?? 
 ?? 
+ ?? 
 ?? 
) ?? + ?? ( )   
 odd values of m. 
 9.  Number  of  prime  factors  of 
 is  when  a,  ?? 
 ?? 
,    ?? 
 ?? 
,    ?? 
 ?? 
,    ??    
 ?? 
    ?? + ?? + ?? + ?? 
 b, c, d are all prime numbers. 
 10.  HCF of  and  = ( ?? 
 ?? 
- 1 ) ( ?? 
 ?? 
- 1 )
 [  ] ( ?? 
 ?????? ( ?? ,    ?? )
- 1 )
 Number of Zeros in an expression 
 We  shall  understand  this  concept  with 
 the help of an example. 
 Let’s  ?nd  the  number  of  zeros  in  the 
 following  expression:  24  32  17  23 × × ×
 19 = (2 
 3 
 × 3 
 1 
 )  2 
 5 
 × 17 × 23 × 19 × × 
 Notice  that  a  zero  is  made  only  when 
 there  is  a  combination  of  2  and  5.  Since 
 there  is  no  ‘5’  here  there  will  be  no  zero  in 
 the above expression. 
 Example:- 
 8     ×     15     ×     23     ×     17     ×     25     ×     22 =
 2 
 3 
× ( 3 
 1 
× 5 
 1 
)    ×     23     ×     17     ×     5 
 2 
×    2 
 1 
    ×     11 
 In  this  expression  there  are  4  twos  and  3 
 ?ves.  From  this  3  pairs  of  can  be  5×2 
 formed.  Therefore,  there  will  be  3  zeros 
 in the ?nal product. 
 Que  .  Find  the  number  of  zeros  in  the 
 value of: 
 2 
 2 
× 5 
 4 
× 4 
 6 
× 10 
 8 
× 6 
 10 
× 15 
 12 
× 8 
 14 
 . × 20 
 16 
× 10 
 18 
× 25 
 20 
 Sol:- 
 2 
 2 
× 5 
 4 
× 4 
 6 
× 10 
 8 
× 6 
 10 
× 15 
 12 
× 8 
 14 
 = × 20 
 16 
× 10 
 18 
× 25 
 20 
 2 
 2 
× 5 
 4 
× 2 
 12 
× 2 
 8 
× 5 
 8 
× 2 
 10 
× 3 
 10 
× 3 
 12 
× 5 
 12 
× 2 
 42 
× 2 
 32 
× 5 
 16 
× 2 
 18 
× 5 
 18 
× 5 
 40 
 Zeros  are  possible  with  a  combination  of 
 2  Here  the  number  of  5’s  are  less  so     ×     5 
 the  number  of  zeros  will  be  limited  to  the 
 number of 5’s. 
 In  this  expression  number  of  ?ves  are: 
 5 
 4 
× 5 
 8 
× 5 
 12 
× 5 
 16 
× 5 
 18 
× 5 
 40 
;
 i.e. 4 + 8 + 12 + 16 + 18 + 40 = 98 
 The number of Zeros in n! 
 To  ?nd  the  number  of  zeros  in  n!,  we 
 divide  “n”  by  5  until  we  get  a  number  less 
 than  5,  and  then  we  add  all  the  quotients 
 so obtained. 
 Que.  Find the number of zeros in 36! . 
 The number of zeros = 7 + 1 = 8. 
 Remainder Theorem 
 Que.  What  will  be  the  remainder  when 
 is divided by 12?  17     ×     23 
 Ans :-  We can express this as: 
 =  17     ×     23  12 + 5 ( ) × 12 + 11 ( )
= 12     ×     12 + 12     ×     11 + 5     ×     12 + 5  ×  11 
 In  the  above  expression  we  will  ?nd  that 
 remainder  will  depend  on  the  last  term 
 i.e.  5     ×     11 
 Now,  .(  )  7.  ?????? 
 5     ×     11 
 12 
=
 So, 
 12     ×     12    +    12        ×     11    +    5     ×     12    +    5     ×     11 
 12 
 and  remainder  is  same  in  both 
 5     ×     11 
 12 
 cases which is 7. 
 Example:-  Remainder when 
 is divided by 12?  1421     ×     1423     ×     1425 
 (  )  ?????? 
 1421     ×     1423     ×     1425 
 12 
  
      
 =  (  )  (  )  ?????? 
 5     ×     7     ×     9 
 12 
=    ?????? 
 35     ×     9 
 12 
 (  ) = ?????? 
 11     ×     9 
 12 
= 3 
 Negative Remainder 
 Taking  a  negative  remainder  will  make 
 our calculation easier. 
 Examples 
 (i)  rem  (  )  =  rem  (  ) 
 7     ×     8 
 9 
- 2        ×    - 1 
 9 
 =  2  1 = 2    - × -
 (ii)  rem  (  ) =  rem  (  ) 
 55     ×     56 
 57 
- 2        × - 1 
 57 
 = - 2  1  × - = 2 
 (iii)  rem  (  ) =  rem  (  ) 
 7     ×     10 
 9 
- 2     ×     1 
 9 
 =  2  1 -    ×    =   - 2     ???? ,    7 
 Large Power Concepts 
 Look at the following examples: 
 (i)  rem (  ) =  (  ) 
 28 
 12345 
 9 
 ?????? 
 27    +    1 ( )
 12345 
 9 
 = rem (  ) = 
 1 
 12345 
 9 
 1 
 12345 
= 1 
 (ii)  rem (  ) 
 26 
 12345 
 9 
 =  (  )  ?????? 
 27    -    1 ( )
 12345 
 9 
 = rem (  ) = -  = - 1  or 8 
- 1 
 12345 
 9 
 1 
 12345 
 Application of Remainder 
 Theorem 
 Que  .  Find  the  last  two  digits  of  the 
 expression 
 ?  22     ×     31     ×     44     ×     27     ×     37     ×     43 
 Sol:-  If  we  divide  the  above  expression  by 
 100,  we  will  get  the  last  two  digits  as 
 remainder. 
 (  )  ,  ?     ?????? 
 22     ×     31     ×     44     ×     27     ×     37     ×     43 
 100 
 dividing by 4 to make it simple 
 (  ) = ?????? 
 22     ×     31     ×     11     ×     27     ×     37     ×     43 
 25 
 (  ) = ?????? 
 132     ×     22     ×     216 
 25 
 (  )  (  ) = ?????? 
 7     ×     22     ×     16 
 25 
             ?     ?????? 
 4     ×     16 
 25 
 (  )    = ?????? 
 14 
 25 
= 14 
 Since  we  had  divided  by  4  initially  now  to 
 get  the  correct  answer,  we  need  to 
 multiply the remainder by 4. 
 So  remainder  will  be  which  14     ×     4 = 56 ,
 will  also  be  the  last  two  digits  of  the 
 expression. 
 Variety Questions 
 Q.1.  A  six-digit  number  11p9q4  is 
 divisible  by  24.  Then  the  greatest 
 possible value for pq is: 
 SSC CGL Tier II  (26/10/2023) 
 (a) 56  (b) 68  (c) 42  (d) 32 
 Q.2.  The  remainder  of  the  term 
 when  divided  9 + 9 
 2 
+............. + 9 
( 2  ??    +    1 )
 by 6 is: 
 SSC CHSL 11/08/2023 (4th Shift) 
 (a) 1  (b) 4  (c) 2  (d) 3 
 Q.3.  Two  numbers,  when  divided  by  a 
 certain  divisor,  leave  the  remainder  57. 
 When  sum  of  the  two  numbers  is  divided 
 by the same divisor, the remainder is 49. 
 The divisor is: 
 SSC CHSL 08/08/2023 (3rd Shift) 
 (a) 56  (b) 57  (c) 49  (d) 65 
 Q.4.  In  a  division  sum,  the  divisor  is  11 
 times  the  quotient  and  5  times  the 
 remainder.  If  the  remainder  is  44,  then 
 the dividend is: 
 SSC CHSL 07/08/2023 (4th Shift) 
 (a) 8888  (b) 4448  (c) 8444   (d) 4444 
 Q.5.  What  is  the  least  value  of  x  +  y,  if  10 
 digit  number  780x533y24  is  divisible  by 
 88 ? 
 SSC CHSL 03/08/2023 (4th Shift) 
 (a) 4  (b) 3  (c) 1  (d) 2 
 Q.6.  During  a  division,  Pranjal  mistakenly 
 took  as  the  dividend  a  number  that  was 
 10%  more  than  the  original  dividend.  He 
 also  mistakenly  took  as  the  divisor  a 
 number  that  was  25%  more  than  the 
 original  divisor.  If  the  correct  quotient  of 
 the  original  division  problem  was  25  and 
 the  remainder  was  0,  what  was  the 
 quotient  that  Pranjal  obtained,  assuming 
 his calculations had no error ? 
 SSC CGL 17/07/2023 (4th shift) 
 (a) 21.75  (b) 21.25   (c) 28.75  (d) 22 
 Q.7.  The  six-digit  number  7x1yyx  is  a 
 multiple  of  33  for  non-zero  digits  x  and  y. 
 Which  of  the  following  could  be  a 
 possible value of (x + y) ? 
 Matriculation Level 30/06/2023 (Shift - 4) 
 (a) 5  (b) 4  (c) 2  (d) 3 
 Q.8.  A  girl  wants  to  plant  trees  in  her 
 garden  in  rows  in  such  a  way  that  the 
 number  of  trees  in  each  row  to  be  the 
 same.  There  are  10  rows  and  the  number 
 of  trees  in  each  row  is  12,  what  is  the 
 number  of  trees  in  each  row,  if  there  are 
 5 more rows ? 
 SSC MTS 17/05/2023 (Evening) 
 (a) 10  (b) 8  (c) 6  (d) 12 
 Q.9.  What  is  the  total  number  of  factors 
 of  the  number  720  except  1  and  the 
 number itself? 
 SSC CHSL 10/03/2023 (4th Shift) 
 (a) 29  (b) 27  (c) 32  (d) 28 
 Q.10.  Which  of  the  following  is  the 
 smallest  among  (  14  )  ,  (  12  )  ,  (  16  ) 
 1 
 3 
 1 
 2 
 1 
 6 
 & 
 (  25  )  ? 
 1 
 12 
 SSC CHSL 10/03/2023 (3rd Shift) 
 (a)  (  14  )  (b)  (  25  )  (c)  (  16  )  (d)  (  12  ) 
 1 
 3 
 1 
 12 
 1 
 6 
 1 
 2 
 Q.11.  Which  of  the  following  statements 
 is correct ? 
 I.The  Value  of  100 
 2 
 -  99 
 2 
 +  98 
 2 
 -  97 
 2 
 +  96 
 2 
 - 95 
 2 
 + 94 
 2 
 - 93 
 2 
 + ...... + 22 
 2 
 - 21 
 2 
 is 4840. 
 II. The value of  (  )  (  ) (  ?? 
 2 
+
 1 
 ?? 
 2 
 ?? -
 1 
 ?? 
 ?? 
 4 
 )(  )(  )  is K 
 16 
 - +
 1 
 ?? 
 4 
 ?? +
 1 
 ?? 
 ?? 
 4 
-
 1 
 ?? 
 4 
 1 
 ?? 
 16 
 SSC CGL 13/12/2022 (3rd Shift) 
 (a) Neither I nor II  (b) Both I and II 
 (c) Only II  (d) Only I 
 Q.12.  If  the  seven-digit  number  52A6B7C 
 is  divisible  by  33,  and  A,  B,  C  are  primes, 
 then the maximum value of 2A+3B+C is: 
 SSC CGL 12/12/2022 (3rd Shift) 
 (a) 32  (b) 23  (c) 27  (d) 34 
 Q.13.  If  the  9  -  digit  number  83P93678Q 
 is  divisible  by  72,  then  what  is  the  value 
 of  ?  ?? 
 2 
+ ?? 
 2 
+ 12    
 SSC CGL  05/12/2022 (4th Shift) 
 (a) 6  (b) 7  (c) 8  (d) 9 
 Q.14.  In  a  test  (+  5)  marks  are  given  for 
 every  correct  answer  and  (-2)  marks  are 
 given  for  every  incorrect  answer.  Jay 
 answered  all  the  questions  and  scored 
 (-12)  marks,  though  he  got  4  correct 
 answers.  How  many  of  his  answers  were 
 INCORRECT ? 
 SSC CPO 11/11/2022 (Evening) 
 (a) 8  (b) 32  (c) 16  (d) 20 
 Q.15.  What  is  the  sum  of  all  the  common 
 terms  between  the  given  series  S1  and 
 S2 ? 
 S1 = 2, 9, 16, ……., 632 
 S2 = 7, 11, 15, ……., 743 
 SSC CGL Tier II  (08/08/2022) 
 (a) 6974  (b) 6750   (c) 7140   (d) 6860 
 Q.16.  If  the  7  -  digit  number  x8942y4  is 
 divisible  by  56,  what  is  the  value  of  (  +  ?? 
 2 
 y)  for  the  largest  value  of  y,  where  x  and  y 
 are natural numbers? 
 SSC CGL 11/04/2022 (Evening) 
 (a) 33  (b) 44  (c) 55  (d) 70 
 Q.17.  Let p, q, r and s be positive natural 
 numbers having three exact factors 
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 Number System 
 Basics of Number System 
 (1).  Face  Value  :  It  is  nothing  but  the 
 number  itself  about  which  it  has  been 
 asked. 
 Eg:  In  the  number  23576,  face  value  of  5 
 is 5 and face value of 7 is 7. 
 (2).  Place  Value  :  The  place  value  of  a 
 number  depends  on  its  position  in  the 
 number.  Each  position  has  a  value  10 
 n 
 , 
 the places to its right. 
 Eg:  In  the  number  23576,  place  value  of  5 
 is 500 and place value of 3 is 3000. 
 Types of Numbers 
 (1). Natural Numbers (N) : 
 All  positive  counting  numbers.  (0  is  not 
 included in it.) 
 Examples: 1, 2, 3, 4 … etc. 
 (2).  Whole  Numbers  (W):  All  non- 
 negative numbers are all whole numbers. 
 Examples: 0, 1, 2, 3, 4… etc. 
 (3).  Integer  Numbers  (I):  All  positive 
 numbers  and  negative  numbers 
 including  zero.  Positive  numbers  are 
 called  positive  integers  and  negative 
 numbers are called negative integers. 
 I = ….. , -4, - 3, - 2, - 1, 0, 1, 2, 3, 4 …... 
 (4).  Even  Numbers  :  2,  4,  6,  8,  10….. 
 [Divisible by 2 completely] 
 (5).  Odd  Numbers  :  1,  3,  5,  7,  9,  11…..  [Not 
 divisible by 2 completely] 
 (6).  Rational  Numbers  :  Numbers  whose 
 exact  value  can  be  determined.  Also  a 
 number  which  can  be  written  in  the  form 
 ,  where  p  and  q  are  integers  and  q  ?  0
 ?? 
 ?? 
 is called a rational  number. For example, 
 Examples :  = 0.75,  = 0.8  ,  , 
 3 
 4 
 4 
 5 
 9 
- 5 
 22 
 7
 (7).  Irrational  Numbers  :  Numbers  whose 
 exact value cannot be determined. 
 Example :  = 3.142857142857 … p
 (8).  Prime  number  :  A  number  which  is 
 divisible  by  1  and  itself.  2  is  only  an  even 
 prime number. 
 Example : 2, 3, 5, 7, 11, etc. 
 Note:- 
 Total prime no. between 1 - 50  15 ?
 Total prime no. between 1 - 100  25 ?
 Total prime no. between 1 - 500  95 ?
 Total prime no. between 1 - 1000  168 ?
 (9).  Composite  number  :  If  we  remove  all 
 prime  numbers  from  natural  numbers 
 then whatever is left is called Composite 
 numbers. 
 Example : 4, 6, 8, 9, 10, 12 etc. 
 Note :-  1 is neither prime nor composite. 
 (10).  Co  -  prime  number  :  Two  numbers 
 are  called  Co-prime  numbers  if  their  HCF 
 is 1. 
 Example  : (2 and 3), (6 and 11). 
 Note  :  Two  prime  numbers  are  always 
 co-prime  numbers  to  each  other.  Any  two 
 consecutive  integers  are  always  co-prime 
 number to each other. 
 Factors 
 The  factors  of  a  number  are  the  numbers 
 that  divide  it  completely  without  leaving 
 any remainder. 
 Example  :  24  can  be  completely  divided 
 by  1,  2,  3,  4,  6,  8,  12  and  24,  so  these 
 numbers are factors of 24. 
 Prime  factorisation  of  a  number  :  When 
 a  number  is  written  in  the  form  of 
 multiplication  of  its  prime  factors,  it's 
 called prime factorisation. 
 Prime factorisation of 24. 
 24  2  2  2  3 or ?   ×      ×   ×    2 
 3 
×    3 
 1
 Number  of  factors  :  To  ?nd  the  number 
 of  factors  we  write  the  number  in  the 
 form  of  prime  factors  and  then  add  +1  to 
 the  exponent  of  prime  factors  and 
 multiply them. 
 For example: 24 =  2 
 3 
×    3 
 1
 Number  of  factors  of  24  (3  +  1)(1  +  1) ?
 = 4  2 = 8. ×
 With  the  help  of  an  example,  we  try  to 
 ?nd the sum of all factors of a number. 
 24 =  ,  2 
 3 
× 3 
 1
 Sum  of  all  factors  =  (  +  )  2 
 0 
+ 2 
 1 
 2 
 2 
+ 2 
 3 
×
 (  ) = 15  4 = 60.  3 
 0 
+ 3 
 1 
×
 Number  of  even  factors  of  a  number  :  To 
 ?nd  the  number  of  even  factors  of  a 
 number,  we  add  +1  to  the  exponents  of 
 prime numbers except 2. 
 (Note  :  If  a  number  doesn't  have  2  as  its 
 factor it will have 0 even factors) 
 Que  .  Find  the  number  of  even  factors  of 
 120. 
 Ans. 120 =  2 
 3 
× 3 
 1 
× 5 
 1
 Number  of  even  factors  =  3  (1  +  1) × ×
 (1 + 1) = 3  2  2 = 12 × ×
 Note :-  To ?nd  the sum of even factors  , 
 we shall ignore  ,  2 
 0 
 Que.  Find the sum of even factors of 120. 
 Sol:-  Sum of even factors = (  + +  )  2 
 1 
    2 
 2 
 2 
 3 
 (  )(  ) = 14  4  6 = 336.  3 
 0 
+ 3 
 1 
 5 
 0 
+    5 
 1 
   ×   ×   
 Number  and  Sum  of  odd  factors  of  a 
 number  :  to  ?nd  the  number  and  sum  of 
 odd  factors  of  a  number,  we  have  to 
 ignore the exponents of 2. 
 Que  . Find the number of odd factors 120. 
 Sol:-  120 =  2 
 3 
× 3 
 1 
× 5 
 1
 Required number = (1 + 1)(1 + 1) = 4 
 The exponent of 2 is completely ignored. 
 Sum  of  odd  factors  of  120  =  (  )(  3 
 0 
+  3 
 1 
 ) = 4  6 = 24  5 
 0 
+ 5 
 1 
   ×
 Some Important Results of Factors: 
 1001 = 7  11  13 ×   ×
 1001  abc = abcabc ×
 1001  234 = 234234 ×
 Que:  Which  of  the  following  is  a  factor  of 
 531531? 
 (a) 15   (b) 13   (c) 11   (d) both b and c
 Sol:-  531531 = 1001  531 ×
 =  7  11  13  531  So,  both  11  and  13 × × ×
 are factors of 531531. 
 111 = 37  3 , 1001  111 = 111111, × ×
 When  a  single  digit  is  written  6  times,  3, 
 7, 11, 13, and 37 are factors of it. 
 Que  .  Which  of  the  following  is  a  factor  of 
 222222 ? 
 (a) 17  (b) 57     (c) 68  (d) 74
 Sol  :- 222222 = 2  111111    ×
 = 2  37 × 3 × 7 ×    11 × 13    ×
 Clearly, 2  37 = 74 is one of the factors. ×
 ? If a, b and c are prime numbers, then
 the number of prime factors of  ?? 
 ?? 
×    ?? 
 ?? 
×
 is (x + y + z).  ?? 
 ?? 
 Recurring Decimal 
 Recurring  decimals  are  referred  to  as 
 numbers  that  are  uniformly  repeated 
 after  the  decimal.  Some  rational 
 numbers  produce  recurring  decimals 
 after  converting  them  into  decimal 
 numbers,  but  all  irrational  numbers 
 produce  recurring  decimals  after 
 converting them into decimal form. 
 Examples : 
 (1)  = 0.3333333 ….. = 0. 
 1 
 3 
 3
 (2) 0.  =  = 1 9 
 9 
 9 
 (3) 0.53  = =  27 
 5327    -    53 
 9900 
 5274 
 9900 
  
      
 (4) 2.53  = 2 +  = 2  27 
 5327    -    53 
 9900 
 5274 
 9900 
 Divisibility Test 
 By  2:-  When  last  digit  is  0  or  an  even 
 number     eg: 520, 588 
 By 3:-  Sum of digits is divisible by 3 
 eg: 1971, 1974 
 By  4:-  When  last  two  digits  are  divisible 
 by 4 or, they are zeros eg: 1528, 1700 
 By 5 :-  When last digit is 0 or 5 
 eg: 1725, 1790 
 By  6  :-  When  the  number  is  divisible  by  2 
 and 3 both. eg: 36, 72 
 By  7  :  -  Subtract  twice  the  last  digit  from 
 the  number  formed  by  the  remaining 
 digits. Like  651 divisible by 7 
 65  -  (1  ×  2)  =  63.  Since  63  is  divisible  by 
 7, so is 651. 
 By  8  :-  When  the  last  three  digits  are 
 divisible by 8.  eg: 2256 
 By  9  :-  When  sum  of  digit  is  divisible  by  9 
 eg: 9216 
 By  10  :-  When  the  last  digit  is  0.  eg: 
 452600 
 By  11:-  When  the  difference  between  the 
 sum  of  odd  and  even  place  digits  is 
 equal to 0 or multiple of 11 . 
 eg: 217382 
 Sum of odd place digits = 2 + 7 + 8 = 17 
 Sum of even place digits = 1 + 3 + 2 = 6 
 17 – 6 = 11, hence 217382 is divisible by 
 11. 
 By  13  :  -  If  adding  four  times  the  last 
 digit  to  the  number  formed  by  the 
 remaining  digits  is  divisible  by  13,  then 
 the  number  is  divisible  by  13.  Like  1326 
 is divisible by 13 
 132  +  (6  4)  =  156.  Repeat  the  same  × 
 process for 156 . 
 15 + (6  4) = 39.so 39 is divisible by 13  × 
 BY  17  :-  The  divisibility  rule  of  17  states, 
 "If  ?ve  times  the  last  digit  is  subtracted 
 from  a  number  made  up  of  the  remaining 
 digits  and  the  remainder  is  either  0  or  a 
 multiple  of  17,  then  the  number  is 
 divisible by 17". 
 Like 221: 22 - 1 × 5 = 17. 
 Prime Number Test 
 For  ?nding  whether  any  number  is  a 
 prime  number  or  not,  we  need  to  ?nd  the 
 nearest  square  root  of  given  number, 
 then  we  need  to  ?nd  out  whether  the 
 given  number  is  divisible  by  any  prime 
 number  less  than  the  obtained  number  or 
 not.  If  it  is  divisible  then  it  is  not  a  prime 
 number and if not divisible then it is a 
 prime number. 
 Example  :  Find  whether  177  is  a  prime 
 number or not. 
 Soln  :  Nearest  square  root  of  177  is  13. 
 Now  we  need  to  check  whether  177  is 
 divisible  by  prime  numbers  less  than  13. 
 On  checking  we  ?nd  that  177  is  divisible 
 by 3. Hence, 177 is not a prime number. 
 Important Formulas 
 1.  Sum of ?rst n natural number 
 s = 
 ?? ( ??    +    1 )
 2 
 2.  Sum of ?rst n odd numbers =  ?? 
 2 
 3.  Sum of ?rst n even numbers 
 =  ?? ( ?? + 1 )
 4.  Sum  of  square  of  ?rst  n  natural 
 numbers = 
 ?? ( ??    +    1 )( 2  ??    +    1 )
 6 
 5.  Sum  of  cubes  of  ?rst  n  natural 
 number = (  ) 
 2 
 ?? ( ??    +    1 )
 2 
 6.  is  divisible  by  for ( ?? 
 ?? 
- ?? 
 ?? 
) ?? - ?? ( )   
 every natural number m. 
 7.  is  divisible  by  and ( ?? 
 ?? 
- ?? 
 ?? 
) ?? + ?? ( )   
 for even values of m.  ?? - ?? ( )
 8.  is  divisible  by  for ( ?? 
 ?? 
+ ?? 
 ?? 
) ?? + ?? ( )   
 odd values of m. 
 9.  Number  of  prime  factors  of 
 is  when  a,  ?? 
 ?? 
,    ?? 
 ?? 
,    ?? 
 ?? 
,    ??    
 ?? 
    ?? + ?? + ?? + ?? 
 b, c, d are all prime numbers. 
 10.  HCF of  and  = ( ?? 
 ?? 
- 1 ) ( ?? 
 ?? 
- 1 )
 [  ] ( ?? 
 ?????? ( ?? ,    ?? )
- 1 )
 Number of Zeros in an expression 
 We  shall  understand  this  concept  with 
 the help of an example. 
 Let’s  ?nd  the  number  of  zeros  in  the 
 following  expression:  24  32  17  23 × × ×
 19 = (2 
 3 
 × 3 
 1 
 )  2 
 5 
 × 17 × 23 × 19 × × 
 Notice  that  a  zero  is  made  only  when 
 there  is  a  combination  of  2  and  5.  Since 
 there  is  no  ‘5’  here  there  will  be  no  zero  in 
 the above expression. 
 Example:- 
 8     ×     15     ×     23     ×     17     ×     25     ×     22 =
 2 
 3 
× ( 3 
 1 
× 5 
 1 
)    ×     23     ×     17     ×     5 
 2 
×    2 
 1 
    ×     11 
 In  this  expression  there  are  4  twos  and  3 
 ?ves.  From  this  3  pairs  of  can  be  5×2 
 formed.  Therefore,  there  will  be  3  zeros 
 in the ?nal product. 
 Que  .  Find  the  number  of  zeros  in  the 
 value of: 
 2 
 2 
× 5 
 4 
× 4 
 6 
× 10 
 8 
× 6 
 10 
× 15 
 12 
× 8 
 14 
 . × 20 
 16 
× 10 
 18 
× 25 
 20 
 Sol:- 
 2 
 2 
× 5 
 4 
× 4 
 6 
× 10 
 8 
× 6 
 10 
× 15 
 12 
× 8 
 14 
 = × 20 
 16 
× 10 
 18 
× 25 
 20 
 2 
 2 
× 5 
 4 
× 2 
 12 
× 2 
 8 
× 5 
 8 
× 2 
 10 
× 3 
 10 
× 3 
 12 
× 5 
 12 
× 2 
 42 
× 2 
 32 
× 5 
 16 
× 2 
 18 
× 5 
 18 
× 5 
 40 
 Zeros  are  possible  with  a  combination  of 
 2  Here  the  number  of  5’s  are  less  so     ×     5 
 the  number  of  zeros  will  be  limited  to  the 
 number of 5’s. 
 In  this  expression  number  of  ?ves  are: 
 5 
 4 
× 5 
 8 
× 5 
 12 
× 5 
 16 
× 5 
 18 
× 5 
 40 
;
 i.e. 4 + 8 + 12 + 16 + 18 + 40 = 98 
 The number of Zeros in n! 
 To  ?nd  the  number  of  zeros  in  n!,  we 
 divide  “n”  by  5  until  we  get  a  number  less 
 than  5,  and  then  we  add  all  the  quotients 
 so obtained. 
 Que.  Find the number of zeros in 36! . 
 The number of zeros = 7 + 1 = 8. 
 Remainder Theorem 
 Que.  What  will  be  the  remainder  when 
 is divided by 12?  17     ×     23 
 Ans :-  We can express this as: 
 =  17     ×     23  12 + 5 ( ) × 12 + 11 ( )
= 12     ×     12 + 12     ×     11 + 5     ×     12 + 5  ×  11 
 In  the  above  expression  we  will  ?nd  that 
 remainder  will  depend  on  the  last  term 
 i.e.  5     ×     11 
 Now,  .(  )  7.  ?????? 
 5     ×     11 
 12 
=
 So, 
 12     ×     12    +    12        ×     11    +    5     ×     12    +    5     ×     11 
 12 
 and  remainder  is  same  in  both 
 5     ×     11 
 12 
 cases which is 7. 
 Example:-  Remainder when 
 is divided by 12?  1421     ×     1423     ×     1425 
 (  )  ?????? 
 1421     ×     1423     ×     1425 
 12 
  
      
 =  (  )  (  )  ?????? 
 5     ×     7     ×     9 
 12 
=    ?????? 
 35     ×     9 
 12 
 (  ) = ?????? 
 11     ×     9 
 12 
= 3 
 Negative Remainder 
 Taking  a  negative  remainder  will  make 
 our calculation easier. 
 Examples 
 (i)  rem  (  )  =  rem  (  ) 
 7     ×     8 
 9 
- 2        ×    - 1 
 9 
 =  2  1 = 2    - × -
 (ii)  rem  (  ) =  rem  (  ) 
 55     ×     56 
 57 
- 2        × - 1 
 57 
 = - 2  1  × - = 2 
 (iii)  rem  (  ) =  rem  (  ) 
 7     ×     10 
 9 
- 2     ×     1 
 9 
 =  2  1 -    ×    =   - 2     ???? ,    7 
 Large Power Concepts 
 Look at the following examples: 
 (i)  rem (  ) =  (  ) 
 28 
 12345 
 9 
 ?????? 
 27    +    1 ( )
 12345 
 9 
 = rem (  ) = 
 1 
 12345 
 9 
 1 
 12345 
= 1 
 (ii)  rem (  ) 
 26 
 12345 
 9 
 =  (  )  ?????? 
 27    -    1 ( )
 12345 
 9 
 = rem (  ) = -  = - 1  or 8 
- 1 
 12345 
 9 
 1 
 12345 
 Application of Remainder 
 Theorem 
 Que  .  Find  the  last  two  digits  of  the 
 expression 
 ?  22     ×     31     ×     44     ×     27     ×     37     ×     43 
 Sol:-  If  we  divide  the  above  expression  by 
 100,  we  will  get  the  last  two  digits  as 
 remainder. 
 (  )  ,  ?     ?????? 
 22     ×     31     ×     44     ×     27     ×     37     ×     43 
 100 
 dividing by 4 to make it simple 
 (  ) = ?????? 
 22     ×     31     ×     11     ×     27     ×     37     ×     43 
 25 
 (  ) = ?????? 
 132     ×     22     ×     216 
 25 
 (  )  (  ) = ?????? 
 7     ×     22     ×     16 
 25 
             ?     ?????? 
 4     ×     16 
 25 
 (  )    = ?????? 
 14 
 25 
= 14 
 Since  we  had  divided  by  4  initially  now  to 
 get  the  correct  answer,  we  need  to 
 multiply the remainder by 4. 
 So  remainder  will  be  which  14     ×     4 = 56 ,
 will  also  be  the  last  two  digits  of  the 
 expression. 
 Variety Questions 
 Q.1.  A  six-digit  number  11p9q4  is 
 divisible  by  24.  Then  the  greatest 
 possible value for pq is: 
 SSC CGL Tier II  (26/10/2023) 
 (a) 56  (b) 68  (c) 42  (d) 32 
 Q.2.  The  remainder  of  the  term 
 when  divided  9 + 9 
 2 
+............. + 9 
( 2  ??    +    1 )
 by 6 is: 
 SSC CHSL 11/08/2023 (4th Shift) 
 (a) 1  (b) 4  (c) 2  (d) 3 
 Q.3.  Two  numbers,  when  divided  by  a 
 certain  divisor,  leave  the  remainder  57. 
 When  sum  of  the  two  numbers  is  divided 
 by the same divisor, the remainder is 49. 
 The divisor is: 
 SSC CHSL 08/08/2023 (3rd Shift) 
 (a) 56  (b) 57  (c) 49  (d) 65 
 Q.4.  In  a  division  sum,  the  divisor  is  11 
 times  the  quotient  and  5  times  the 
 remainder.  If  the  remainder  is  44,  then 
 the dividend is: 
 SSC CHSL 07/08/2023 (4th Shift) 
 (a) 8888  (b) 4448  (c) 8444   (d) 4444 
 Q.5.  What  is  the  least  value  of  x  +  y,  if  10 
 digit  number  780x533y24  is  divisible  by 
 88 ? 
 SSC CHSL 03/08/2023 (4th Shift) 
 (a) 4  (b) 3  (c) 1  (d) 2 
 Q.6.  During  a  division,  Pranjal  mistakenly 
 took  as  the  dividend  a  number  that  was 
 10%  more  than  the  original  dividend.  He 
 also  mistakenly  took  as  the  divisor  a 
 number  that  was  25%  more  than  the 
 original  divisor.  If  the  correct  quotient  of 
 the  original  division  problem  was  25  and 
 the  remainder  was  0,  what  was  the 
 quotient  that  Pranjal  obtained,  assuming 
 his calculations had no error ? 
 SSC CGL 17/07/2023 (4th shift) 
 (a) 21.75  (b) 21.25   (c) 28.75  (d) 22 
 Q.7.  The  six-digit  number  7x1yyx  is  a 
 multiple  of  33  for  non-zero  digits  x  and  y. 
 Which  of  the  following  could  be  a 
 possible value of (x + y) ? 
 Matriculation Level 30/06/2023 (Shift - 4) 
 (a) 5  (b) 4  (c) 2  (d) 3 
 Q.8.  A  girl  wants  to  plant  trees  in  her 
 garden  in  rows  in  such  a  way  that  the 
 number  of  trees  in  each  row  to  be  the 
 same.  There  are  10  rows  and  the  number 
 of  trees  in  each  row  is  12,  what  is  the 
 number  of  trees  in  each  row,  if  there  are 
 5 more rows ? 
 SSC MTS 17/05/2023 (Evening) 
 (a) 10  (b) 8  (c) 6  (d) 12 
 Q.9.  What  is  the  total  number  of  factors 
 of  the  number  720  except  1  and  the 
 number itself? 
 SSC CHSL 10/03/2023 (4th Shift) 
 (a) 29  (b) 27  (c) 32  (d) 28 
 Q.10.  Which  of  the  following  is  the 
 smallest  among  (  14  )  ,  (  12  )  ,  (  16  ) 
 1 
 3 
 1 
 2 
 1 
 6 
 & 
 (  25  )  ? 
 1 
 12 
 SSC CHSL 10/03/2023 (3rd Shift) 
 (a)  (  14  )  (b)  (  25  )  (c)  (  16  )  (d)  (  12  ) 
 1 
 3 
 1 
 12 
 1 
 6 
 1 
 2 
 Q.11.  Which  of  the  following  statements 
 is correct ? 
 I.The  Value  of  100 
 2 
 -  99 
 2 
 +  98 
 2 
 -  97 
 2 
 +  96 
 2 
 - 95 
 2 
 + 94 
 2 
 - 93 
 2 
 + ...... + 22 
 2 
 - 21 
 2 
 is 4840. 
 II. The value of  (  )  (  ) (  ?? 
 2 
+
 1 
 ?? 
 2 
 ?? -
 1 
 ?? 
 ?? 
 4 
 )(  )(  )  is K 
 16 
 - +
 1 
 ?? 
 4 
 ?? +
 1 
 ?? 
 ?? 
 4 
-
 1 
 ?? 
 4 
 1 
 ?? 
 16 
 SSC CGL 13/12/2022 (3rd Shift) 
 (a) Neither I nor II  (b) Both I and II 
 (c) Only II  (d) Only I 
 Q.12.  If  the  seven-digit  number  52A6B7C 
 is  divisible  by  33,  and  A,  B,  C  are  primes, 
 then the maximum value of 2A+3B+C is: 
 SSC CGL 12/12/2022 (3rd Shift) 
 (a) 32  (b) 23  (c) 27  (d) 34 
 Q.13.  If  the  9  -  digit  number  83P93678Q 
 is  divisible  by  72,  then  what  is  the  value 
 of  ?  ?? 
 2 
+ ?? 
 2 
+ 12    
 SSC CGL  05/12/2022 (4th Shift) 
 (a) 6  (b) 7  (c) 8  (d) 9 
 Q.14.  In  a  test  (+  5)  marks  are  given  for 
 every  correct  answer  and  (-2)  marks  are 
 given  for  every  incorrect  answer.  Jay 
 answered  all  the  questions  and  scored 
 (-12)  marks,  though  he  got  4  correct 
 answers.  How  many  of  his  answers  were 
 INCORRECT ? 
 SSC CPO 11/11/2022 (Evening) 
 (a) 8  (b) 32  (c) 16  (d) 20 
 Q.15.  What  is  the  sum  of  all  the  common 
 terms  between  the  given  series  S1  and 
 S2 ? 
 S1 = 2, 9, 16, ……., 632 
 S2 = 7, 11, 15, ……., 743 
 SSC CGL Tier II  (08/08/2022) 
 (a) 6974  (b) 6750   (c) 7140   (d) 6860 
 Q.16.  If  the  7  -  digit  number  x8942y4  is 
 divisible  by  56,  what  is  the  value  of  (  +  ?? 
 2 
 y)  for  the  largest  value  of  y,  where  x  and  y 
 are natural numbers? 
 SSC CGL 11/04/2022 (Evening) 
 (a) 33  (b) 44  (c) 55  (d) 70 
 Q.17.  Let p, q, r and s be positive natural 
 numbers having three exact factors 
 www.ssccglpinnacle.com                                                 Download Pinnacle Exam Preparation App 3
 Pinnacle  Day: 1st - 5th  Number System 
 including  1  and  the  number  itself  If  q  >  p 
 and  both  are  two-digit  numbers,  and  r  >  s 
 and  both  are  one-digit  numbers,  then  the 
 value of the expression  is: 
 ??    -    ??    -    1 
 ??    -    ?? 
 SSC CGL Tier II  (03/02/2022) 
 (a) - s - 1   (b) s - 1   (c) 1 - s   (d) s + 1 
 Q.18.  Three  fractions  x,  y  and  z  are  such 
 that  x  >  y  >  z.  When  the  smallest  of  them 
 is  divided  by  the  greatest,  the  result  is 
 which  exceeds  y  by  0.0625.  If  x  +  y  + 
 9 
 16 
 z = 2  , then what is the value of x + z ? 
 3 
 12 
 SSC CGL Tier II  (29/01/2022) 
 (a)  (b)  (c)  (d) 
 5 
 4 
 1 
 4 
 7 
 4 
 3 
 4 
 Q.19.  The  six-digit  number  537xy5  is 
 divisible by 125. How many such six - 
 digit numbers are there? 
 SSC CHSL 19/04/2021 (Morning) 
 (a) 4  (b) 2  (c) 3  (d) 5 
 Q.20.  How  many  numbers  between  400 
 and 700 are divisible by 5, 6 and 7 ? 
 SSC CPO 24/11/2020 (Evening) 
 (a) 2  (b) 5  (c) 10  (d) 20 
 Q.21.  Find the number of prime factors in 
 the product  . ( 30 )
 5 
× ( 24 )
 5 
 SSC CGL Tier II (18/11/2020) 
 (a) 45  (b) 35  (c) 10  (d) 30 
 Q.22.  Let  ab,  a  b,  is  a  2-digit  prime ?
 number  such  that  ba  is  also  a  prime 
 number. The sum of all such number is: 
 SSC CGL Tier  II (16/11/2020) 
 (a) 374  (b) 418  (c) 407  (d) 396 
 Q.23.  Given  that  2 
 20 
 +  1  is  completely 
 divisible  by  a  whole  number.  Which  of  the 
 following  is  completely  divisible  by  the 
 same number ? 
 SSC CHSL 16/10/2020 (Afternoon) 
 (a)  2 
 15 
 + 1  (b) 5  2 
 30 
×
 (c) 2 
 90 
 + 1  (d)  2 
 60 
 + 1 
 Q.24.  Which  of  the  following  numbers 
 will completely divide 7 
 81 
 + 7 
 82 
 + 7 
 83 
 ? 
 SSC CHSL  17/03/2020 (Morning) 
 (a) 399  (b) 389  (c) 387       (d) 397 
 Q.25.  When  a  positive  integer  is  divided 
 by  d,  the  remainder  is  15.  When  ten  times 
 of  the  same  number  is  divided  by  d,  the 
 remainder  is  6.  The  least  possible  value 
 of d is: 
 SSC CGL 05/03/2020 (Afternoon) 
 (a) 9  (b) 12  (c) 16  (d) 18 
 Q.26.  When  200  is  divided  by  a  positive 
 integer  x,  the  remainder  is  8.  How  many 
 values of x are there? 
 SSC CGL 03/03/2020 (Afternoon) 
 (a) 7  (b) 5  (c) 8  (d) 6 
 Q.27.  The number 1563241234351 is : 
 SSC CPO  13/12/2019 (Evening) 
 (a) divisible by both 3 and 11 
 (b) divisible by 11 but not by 3 
 (c) neither divisible by 3 nor by 11 
 (d) divisible by 3 but not by 11 
 Q.28.  How  many  natural  numbers  less 
 than  1000  are  divisible  by  5  or  7  but  NOT 
 by 35 ? 
 SSC CPO  11/12/2019 (Morning) 
 (a) 285  (b) 313  (c) 341  (d) 243 
 Q.29.  If  r  is  the  remainder  when  each  of 
 4749,  5601  and  7092  is  divided  by  the 
 greatest  possible  number  d  (  1),  then  > 
 the value of (d + r) will be: 
 SSC CPO  11/12/2019 (Morning) 
 (a) 276  (b) 271  (c) 298  (d) 282 
 Q.30.  Let  x  be  the  least  4-digit  number 
 which  when  divided  by  2,  3,  4,  5,  6  and  7 
 leaves  a  remainder  of  1  in  each  case.  If  x 
 lies  between  2800  and  3000,  then  what  is 
 the sum of digits of x ? 
 SSC CPO  09/12/2019 (Evening) 
 (a) 15  (b) 16  (c) 12  (d) 13 
 Q.31.  If  the  six  digit  number  479xyz  is 
 exactly  divisible  by  7,  11  and  13  ,  then  {(  y 
 + z ) ÷ x} is equal to : 
 SSC CPO  09/12/2019 (Morning) 
 (a)  (b) 4  (c)  (d) 
 11 
 9 
 13 
 7 
 7 
 13 
 Q.32.  Which  among  the  following  is  the 
 smallest? 
 SSC CPO 09/12/19 (Morning) 
 (a) v401 - v399     (b) v101 - v99 
 (c) v301 - v299     (d) v201 - v199 
 Q.33.  If  x  is  the  remainder  when  3 
 61284 
 is 
 divided  by  5  and  y  is  the  remainder  when 
 4 
 96 
 is  divided  by  6,  then  what  is  the  value 
 of (2x - y) ? 
 SSC CGL Tier II (13/09/2019) 
 (a) - 4  (b) 4        (c) -2  (d) 2 
 Q.34.  In  ?nding  the  HCF  of  two  numbers 
 by  division  method,  the  last  divisor  is  17 
 and  the  quotients  are  1,  11  and  2, 
 respectively.  What  is  the  sum  of  the  two 
 numbers ? 
 SSC CGL Tier II (13/09/2019) 
 (a) 833  (b) 867  (c) 816  (d) 901 
 Q.35.  Two  positive  numbers  differ  by 
 2001.  When  the  larger  number  is  divided 
 by  the  smaller  number,  the  quotient  is  9 
 and  the  remainder  is  41.  The  sum  of  the 
 digits of the larger number is : 
 SSC CGL Tier II (13/09/2019) 
 (a) 15  (b) 11  (c) 10  (d) 14 
 Q.36.  When  a  two-digit  number  is 
 multiplied  by  the  sum  of  its  digits,  the 
 product  is  424.  When  the  number 
 obtained  by  interchanging  its  digits  is 
 multiplied  by  the  sum  of  the  digits,  the 
 result  is  280.  The  sum  of  the  digits  of  the 
 given number is : 
 SSC CGL Tier II (12/09/2019) 
 (a) 6  (b) 9  (c) 8  (d) 7 
 Q.37.  Let  x  be  the  least  number  which 
 when  divided  by  15,18,20  and  27,  the 
 remainder  in  each  case  is  10  and  x  is  a 
 multiple  of  31.  What  least  number  should 
 be added to x to make it a perfect square ? 
 SSC CGL Tier II (12/09/2019) 
 (a) 39  (b) 37  (c) 43  (d) 36 
 Q.38.  The number of factors of 3600 is : 
 SSC CGL Tier II  (12/09/2019) 
 (a) 45  (b) 44  (c) 43  (d) 42 
 Q.39.  When  12,  16,  18,  20  and  25  divide 
 the  least  number  x,  the  remainder  in  each 
 case  is  4  but  x  is  divisible  by  7.  What  is 
 the digit at the thousands’ place in x ? 
 SSC CGL Tier II  (11/09/2019) 
 (a) 5  (b) 8  (c) 4  (d) 3 
 Q.40.  One  of  the  factors  of  (  ),  8 
 2  ?? 
+ 5 
 2  ?? 
 where k is an odd number, is : 
 SSC CGL Tier II (11/09/2019) 
 (a) 86  (b) 88  (c) 84  (d) 89 
 Q.41.  Let  x  = ( 633 )
 24 
- ( 277 )
 38 
+
 What is the unit digit of x ? ( 266 )
 54 
 SSC CGL Tier  II  (11/09/2019) 
 (a) 7  (b) 6  (c) 4  (d) 8 
 Q.42.  The  sum  of  the  digits  of  a  two-digit 
 number  is  of  the  number.  The  unit 
 1 
 7 
 digit  is  4  less  than  the  tens  digit.  If  the 
 number  obtained  on  reversing  its  digit  is 
 divided by 7, the remainder will be : 
 SSC CGL Tier  II  (11/09/2019) 
 (a) 4  (b) 5  (c) 1  (d) 6 
 Q.43.  When  6892,  7105  and  7531  are 
 divided  by  the  greatest  number  x,  then 
 the  remainder  in  each  case  is  y.  What  is 
 the value of (x - y) ? 
 SSC MTS 22/08/2019 (Afternoon) 
 (a) 123  (b) 137  (c) 147    (d) 113 
 Q.44.  Let  x  be  the  greatest  number  which 
 when  divides  6475,  4984  and  4132,  the 
 remainder  in  each  case  is  the  same. 
 What is the sum of digits of x? 
 SSC MTS 22/08/2019 (Morning) 
 (a) 4  (b) 7  (c) 5  (d) 6 
 Q.45.  When  an  integer  n  is  divided  by  8, 
 the  remainder  is  3.  What  will  be  the 
 remainder if 6n - 1 is divided by 8 ? 
 SSC CGL 13/06/2019 (Evening) 
 www.ssccglpinnacle.com                                                 Download Pinnacle Exam Preparation App 4
Page 5


      
 Number System 
 Basics of Number System 
 (1).  Face  Value  :  It  is  nothing  but  the 
 number  itself  about  which  it  has  been 
 asked. 
 Eg:  In  the  number  23576,  face  value  of  5 
 is 5 and face value of 7 is 7. 
 (2).  Place  Value  :  The  place  value  of  a 
 number  depends  on  its  position  in  the 
 number.  Each  position  has  a  value  10 
 n 
 , 
 the places to its right. 
 Eg:  In  the  number  23576,  place  value  of  5 
 is 500 and place value of 3 is 3000. 
 Types of Numbers 
 (1). Natural Numbers (N) : 
 All  positive  counting  numbers.  (0  is  not 
 included in it.) 
 Examples: 1, 2, 3, 4 … etc. 
 (2).  Whole  Numbers  (W):  All  non- 
 negative numbers are all whole numbers. 
 Examples: 0, 1, 2, 3, 4… etc. 
 (3).  Integer  Numbers  (I):  All  positive 
 numbers  and  negative  numbers 
 including  zero.  Positive  numbers  are 
 called  positive  integers  and  negative 
 numbers are called negative integers. 
 I = ….. , -4, - 3, - 2, - 1, 0, 1, 2, 3, 4 …... 
 (4).  Even  Numbers  :  2,  4,  6,  8,  10….. 
 [Divisible by 2 completely] 
 (5).  Odd  Numbers  :  1,  3,  5,  7,  9,  11…..  [Not 
 divisible by 2 completely] 
 (6).  Rational  Numbers  :  Numbers  whose 
 exact  value  can  be  determined.  Also  a 
 number  which  can  be  written  in  the  form 
 ,  where  p  and  q  are  integers  and  q  ?  0
 ?? 
 ?? 
 is called a rational  number. For example, 
 Examples :  = 0.75,  = 0.8  ,  , 
 3 
 4 
 4 
 5 
 9 
- 5 
 22 
 7
 (7).  Irrational  Numbers  :  Numbers  whose 
 exact value cannot be determined. 
 Example :  = 3.142857142857 … p
 (8).  Prime  number  :  A  number  which  is 
 divisible  by  1  and  itself.  2  is  only  an  even 
 prime number. 
 Example : 2, 3, 5, 7, 11, etc. 
 Note:- 
 Total prime no. between 1 - 50  15 ?
 Total prime no. between 1 - 100  25 ?
 Total prime no. between 1 - 500  95 ?
 Total prime no. between 1 - 1000  168 ?
 (9).  Composite  number  :  If  we  remove  all 
 prime  numbers  from  natural  numbers 
 then whatever is left is called Composite 
 numbers. 
 Example : 4, 6, 8, 9, 10, 12 etc. 
 Note :-  1 is neither prime nor composite. 
 (10).  Co  -  prime  number  :  Two  numbers 
 are  called  Co-prime  numbers  if  their  HCF 
 is 1. 
 Example  : (2 and 3), (6 and 11). 
 Note  :  Two  prime  numbers  are  always 
 co-prime  numbers  to  each  other.  Any  two 
 consecutive  integers  are  always  co-prime 
 number to each other. 
 Factors 
 The  factors  of  a  number  are  the  numbers 
 that  divide  it  completely  without  leaving 
 any remainder. 
 Example  :  24  can  be  completely  divided 
 by  1,  2,  3,  4,  6,  8,  12  and  24,  so  these 
 numbers are factors of 24. 
 Prime  factorisation  of  a  number  :  When 
 a  number  is  written  in  the  form  of 
 multiplication  of  its  prime  factors,  it's 
 called prime factorisation. 
 Prime factorisation of 24. 
 24  2  2  2  3 or ?   ×      ×   ×    2 
 3 
×    3 
 1
 Number  of  factors  :  To  ?nd  the  number 
 of  factors  we  write  the  number  in  the 
 form  of  prime  factors  and  then  add  +1  to 
 the  exponent  of  prime  factors  and 
 multiply them. 
 For example: 24 =  2 
 3 
×    3 
 1
 Number  of  factors  of  24  (3  +  1)(1  +  1) ?
 = 4  2 = 8. ×
 With  the  help  of  an  example,  we  try  to 
 ?nd the sum of all factors of a number. 
 24 =  ,  2 
 3 
× 3 
 1
 Sum  of  all  factors  =  (  +  )  2 
 0 
+ 2 
 1 
 2 
 2 
+ 2 
 3 
×
 (  ) = 15  4 = 60.  3 
 0 
+ 3 
 1 
×
 Number  of  even  factors  of  a  number  :  To 
 ?nd  the  number  of  even  factors  of  a 
 number,  we  add  +1  to  the  exponents  of 
 prime numbers except 2. 
 (Note  :  If  a  number  doesn't  have  2  as  its 
 factor it will have 0 even factors) 
 Que  .  Find  the  number  of  even  factors  of 
 120. 
 Ans. 120 =  2 
 3 
× 3 
 1 
× 5 
 1
 Number  of  even  factors  =  3  (1  +  1) × ×
 (1 + 1) = 3  2  2 = 12 × ×
 Note :-  To ?nd  the sum of even factors  , 
 we shall ignore  ,  2 
 0 
 Que.  Find the sum of even factors of 120. 
 Sol:-  Sum of even factors = (  + +  )  2 
 1 
    2 
 2 
 2 
 3 
 (  )(  ) = 14  4  6 = 336.  3 
 0 
+ 3 
 1 
 5 
 0 
+    5 
 1 
   ×   ×   
 Number  and  Sum  of  odd  factors  of  a 
 number  :  to  ?nd  the  number  and  sum  of 
 odd  factors  of  a  number,  we  have  to 
 ignore the exponents of 2. 
 Que  . Find the number of odd factors 120. 
 Sol:-  120 =  2 
 3 
× 3 
 1 
× 5 
 1
 Required number = (1 + 1)(1 + 1) = 4 
 The exponent of 2 is completely ignored. 
 Sum  of  odd  factors  of  120  =  (  )(  3 
 0 
+  3 
 1 
 ) = 4  6 = 24  5 
 0 
+ 5 
 1 
   ×
 Some Important Results of Factors: 
 1001 = 7  11  13 ×   ×
 1001  abc = abcabc ×
 1001  234 = 234234 ×
 Que:  Which  of  the  following  is  a  factor  of 
 531531? 
 (a) 15   (b) 13   (c) 11   (d) both b and c
 Sol:-  531531 = 1001  531 ×
 =  7  11  13  531  So,  both  11  and  13 × × ×
 are factors of 531531. 
 111 = 37  3 , 1001  111 = 111111, × ×
 When  a  single  digit  is  written  6  times,  3, 
 7, 11, 13, and 37 are factors of it. 
 Que  .  Which  of  the  following  is  a  factor  of 
 222222 ? 
 (a) 17  (b) 57     (c) 68  (d) 74
 Sol  :- 222222 = 2  111111    ×
 = 2  37 × 3 × 7 ×    11 × 13    ×
 Clearly, 2  37 = 74 is one of the factors. ×
 ? If a, b and c are prime numbers, then
 the number of prime factors of  ?? 
 ?? 
×    ?? 
 ?? 
×
 is (x + y + z).  ?? 
 ?? 
 Recurring Decimal 
 Recurring  decimals  are  referred  to  as 
 numbers  that  are  uniformly  repeated 
 after  the  decimal.  Some  rational 
 numbers  produce  recurring  decimals 
 after  converting  them  into  decimal 
 numbers,  but  all  irrational  numbers 
 produce  recurring  decimals  after 
 converting them into decimal form. 
 Examples : 
 (1)  = 0.3333333 ….. = 0. 
 1 
 3 
 3
 (2) 0.  =  = 1 9 
 9 
 9 
 (3) 0.53  = =  27 
 5327    -    53 
 9900 
 5274 
 9900 
  
      
 (4) 2.53  = 2 +  = 2  27 
 5327    -    53 
 9900 
 5274 
 9900 
 Divisibility Test 
 By  2:-  When  last  digit  is  0  or  an  even 
 number     eg: 520, 588 
 By 3:-  Sum of digits is divisible by 3 
 eg: 1971, 1974 
 By  4:-  When  last  two  digits  are  divisible 
 by 4 or, they are zeros eg: 1528, 1700 
 By 5 :-  When last digit is 0 or 5 
 eg: 1725, 1790 
 By  6  :-  When  the  number  is  divisible  by  2 
 and 3 both. eg: 36, 72 
 By  7  :  -  Subtract  twice  the  last  digit  from 
 the  number  formed  by  the  remaining 
 digits. Like  651 divisible by 7 
 65  -  (1  ×  2)  =  63.  Since  63  is  divisible  by 
 7, so is 651. 
 By  8  :-  When  the  last  three  digits  are 
 divisible by 8.  eg: 2256 
 By  9  :-  When  sum  of  digit  is  divisible  by  9 
 eg: 9216 
 By  10  :-  When  the  last  digit  is  0.  eg: 
 452600 
 By  11:-  When  the  difference  between  the 
 sum  of  odd  and  even  place  digits  is 
 equal to 0 or multiple of 11 . 
 eg: 217382 
 Sum of odd place digits = 2 + 7 + 8 = 17 
 Sum of even place digits = 1 + 3 + 2 = 6 
 17 – 6 = 11, hence 217382 is divisible by 
 11. 
 By  13  :  -  If  adding  four  times  the  last 
 digit  to  the  number  formed  by  the 
 remaining  digits  is  divisible  by  13,  then 
 the  number  is  divisible  by  13.  Like  1326 
 is divisible by 13 
 132  +  (6  4)  =  156.  Repeat  the  same  × 
 process for 156 . 
 15 + (6  4) = 39.so 39 is divisible by 13  × 
 BY  17  :-  The  divisibility  rule  of  17  states, 
 "If  ?ve  times  the  last  digit  is  subtracted 
 from  a  number  made  up  of  the  remaining 
 digits  and  the  remainder  is  either  0  or  a 
 multiple  of  17,  then  the  number  is 
 divisible by 17". 
 Like 221: 22 - 1 × 5 = 17. 
 Prime Number Test 
 For  ?nding  whether  any  number  is  a 
 prime  number  or  not,  we  need  to  ?nd  the 
 nearest  square  root  of  given  number, 
 then  we  need  to  ?nd  out  whether  the 
 given  number  is  divisible  by  any  prime 
 number  less  than  the  obtained  number  or 
 not.  If  it  is  divisible  then  it  is  not  a  prime 
 number and if not divisible then it is a 
 prime number. 
 Example  :  Find  whether  177  is  a  prime 
 number or not. 
 Soln  :  Nearest  square  root  of  177  is  13. 
 Now  we  need  to  check  whether  177  is 
 divisible  by  prime  numbers  less  than  13. 
 On  checking  we  ?nd  that  177  is  divisible 
 by 3. Hence, 177 is not a prime number. 
 Important Formulas 
 1.  Sum of ?rst n natural number 
 s = 
 ?? ( ??    +    1 )
 2 
 2.  Sum of ?rst n odd numbers =  ?? 
 2 
 3.  Sum of ?rst n even numbers 
 =  ?? ( ?? + 1 )
 4.  Sum  of  square  of  ?rst  n  natural 
 numbers = 
 ?? ( ??    +    1 )( 2  ??    +    1 )
 6 
 5.  Sum  of  cubes  of  ?rst  n  natural 
 number = (  ) 
 2 
 ?? ( ??    +    1 )
 2 
 6.  is  divisible  by  for ( ?? 
 ?? 
- ?? 
 ?? 
) ?? - ?? ( )   
 every natural number m. 
 7.  is  divisible  by  and ( ?? 
 ?? 
- ?? 
 ?? 
) ?? + ?? ( )   
 for even values of m.  ?? - ?? ( )
 8.  is  divisible  by  for ( ?? 
 ?? 
+ ?? 
 ?? 
) ?? + ?? ( )   
 odd values of m. 
 9.  Number  of  prime  factors  of 
 is  when  a,  ?? 
 ?? 
,    ?? 
 ?? 
,    ?? 
 ?? 
,    ??    
 ?? 
    ?? + ?? + ?? + ?? 
 b, c, d are all prime numbers. 
 10.  HCF of  and  = ( ?? 
 ?? 
- 1 ) ( ?? 
 ?? 
- 1 )
 [  ] ( ?? 
 ?????? ( ?? ,    ?? )
- 1 )
 Number of Zeros in an expression 
 We  shall  understand  this  concept  with 
 the help of an example. 
 Let’s  ?nd  the  number  of  zeros  in  the 
 following  expression:  24  32  17  23 × × ×
 19 = (2 
 3 
 × 3 
 1 
 )  2 
 5 
 × 17 × 23 × 19 × × 
 Notice  that  a  zero  is  made  only  when 
 there  is  a  combination  of  2  and  5.  Since 
 there  is  no  ‘5’  here  there  will  be  no  zero  in 
 the above expression. 
 Example:- 
 8     ×     15     ×     23     ×     17     ×     25     ×     22 =
 2 
 3 
× ( 3 
 1 
× 5 
 1 
)    ×     23     ×     17     ×     5 
 2 
×    2 
 1 
    ×     11 
 In  this  expression  there  are  4  twos  and  3 
 ?ves.  From  this  3  pairs  of  can  be  5×2 
 formed.  Therefore,  there  will  be  3  zeros 
 in the ?nal product. 
 Que  .  Find  the  number  of  zeros  in  the 
 value of: 
 2 
 2 
× 5 
 4 
× 4 
 6 
× 10 
 8 
× 6 
 10 
× 15 
 12 
× 8 
 14 
 . × 20 
 16 
× 10 
 18 
× 25 
 20 
 Sol:- 
 2 
 2 
× 5 
 4 
× 4 
 6 
× 10 
 8 
× 6 
 10 
× 15 
 12 
× 8 
 14 
 = × 20 
 16 
× 10 
 18 
× 25 
 20 
 2 
 2 
× 5 
 4 
× 2 
 12 
× 2 
 8 
× 5 
 8 
× 2 
 10 
× 3 
 10 
× 3 
 12 
× 5 
 12 
× 2 
 42 
× 2 
 32 
× 5 
 16 
× 2 
 18 
× 5 
 18 
× 5 
 40 
 Zeros  are  possible  with  a  combination  of 
 2  Here  the  number  of  5’s  are  less  so     ×     5 
 the  number  of  zeros  will  be  limited  to  the 
 number of 5’s. 
 In  this  expression  number  of  ?ves  are: 
 5 
 4 
× 5 
 8 
× 5 
 12 
× 5 
 16 
× 5 
 18 
× 5 
 40 
;
 i.e. 4 + 8 + 12 + 16 + 18 + 40 = 98 
 The number of Zeros in n! 
 To  ?nd  the  number  of  zeros  in  n!,  we 
 divide  “n”  by  5  until  we  get  a  number  less 
 than  5,  and  then  we  add  all  the  quotients 
 so obtained. 
 Que.  Find the number of zeros in 36! . 
 The number of zeros = 7 + 1 = 8. 
 Remainder Theorem 
 Que.  What  will  be  the  remainder  when 
 is divided by 12?  17     ×     23 
 Ans :-  We can express this as: 
 =  17     ×     23  12 + 5 ( ) × 12 + 11 ( )
= 12     ×     12 + 12     ×     11 + 5     ×     12 + 5  ×  11 
 In  the  above  expression  we  will  ?nd  that 
 remainder  will  depend  on  the  last  term 
 i.e.  5     ×     11 
 Now,  .(  )  7.  ?????? 
 5     ×     11 
 12 
=
 So, 
 12     ×     12    +    12        ×     11    +    5     ×     12    +    5     ×     11 
 12 
 and  remainder  is  same  in  both 
 5     ×     11 
 12 
 cases which is 7. 
 Example:-  Remainder when 
 is divided by 12?  1421     ×     1423     ×     1425 
 (  )  ?????? 
 1421     ×     1423     ×     1425 
 12 
  
      
 =  (  )  (  )  ?????? 
 5     ×     7     ×     9 
 12 
=    ?????? 
 35     ×     9 
 12 
 (  ) = ?????? 
 11     ×     9 
 12 
= 3 
 Negative Remainder 
 Taking  a  negative  remainder  will  make 
 our calculation easier. 
 Examples 
 (i)  rem  (  )  =  rem  (  ) 
 7     ×     8 
 9 
- 2        ×    - 1 
 9 
 =  2  1 = 2    - × -
 (ii)  rem  (  ) =  rem  (  ) 
 55     ×     56 
 57 
- 2        × - 1 
 57 
 = - 2  1  × - = 2 
 (iii)  rem  (  ) =  rem  (  ) 
 7     ×     10 
 9 
- 2     ×     1 
 9 
 =  2  1 -    ×    =   - 2     ???? ,    7 
 Large Power Concepts 
 Look at the following examples: 
 (i)  rem (  ) =  (  ) 
 28 
 12345 
 9 
 ?????? 
 27    +    1 ( )
 12345 
 9 
 = rem (  ) = 
 1 
 12345 
 9 
 1 
 12345 
= 1 
 (ii)  rem (  ) 
 26 
 12345 
 9 
 =  (  )  ?????? 
 27    -    1 ( )
 12345 
 9 
 = rem (  ) = -  = - 1  or 8 
- 1 
 12345 
 9 
 1 
 12345 
 Application of Remainder 
 Theorem 
 Que  .  Find  the  last  two  digits  of  the 
 expression 
 ?  22     ×     31     ×     44     ×     27     ×     37     ×     43 
 Sol:-  If  we  divide  the  above  expression  by 
 100,  we  will  get  the  last  two  digits  as 
 remainder. 
 (  )  ,  ?     ?????? 
 22     ×     31     ×     44     ×     27     ×     37     ×     43 
 100 
 dividing by 4 to make it simple 
 (  ) = ?????? 
 22     ×     31     ×     11     ×     27     ×     37     ×     43 
 25 
 (  ) = ?????? 
 132     ×     22     ×     216 
 25 
 (  )  (  ) = ?????? 
 7     ×     22     ×     16 
 25 
             ?     ?????? 
 4     ×     16 
 25 
 (  )    = ?????? 
 14 
 25 
= 14 
 Since  we  had  divided  by  4  initially  now  to 
 get  the  correct  answer,  we  need  to 
 multiply the remainder by 4. 
 So  remainder  will  be  which  14     ×     4 = 56 ,
 will  also  be  the  last  two  digits  of  the 
 expression. 
 Variety Questions 
 Q.1.  A  six-digit  number  11p9q4  is 
 divisible  by  24.  Then  the  greatest 
 possible value for pq is: 
 SSC CGL Tier II  (26/10/2023) 
 (a) 56  (b) 68  (c) 42  (d) 32 
 Q.2.  The  remainder  of  the  term 
 when  divided  9 + 9 
 2 
+............. + 9 
( 2  ??    +    1 )
 by 6 is: 
 SSC CHSL 11/08/2023 (4th Shift) 
 (a) 1  (b) 4  (c) 2  (d) 3 
 Q.3.  Two  numbers,  when  divided  by  a 
 certain  divisor,  leave  the  remainder  57. 
 When  sum  of  the  two  numbers  is  divided 
 by the same divisor, the remainder is 49. 
 The divisor is: 
 SSC CHSL 08/08/2023 (3rd Shift) 
 (a) 56  (b) 57  (c) 49  (d) 65 
 Q.4.  In  a  division  sum,  the  divisor  is  11 
 times  the  quotient  and  5  times  the 
 remainder.  If  the  remainder  is  44,  then 
 the dividend is: 
 SSC CHSL 07/08/2023 (4th Shift) 
 (a) 8888  (b) 4448  (c) 8444   (d) 4444 
 Q.5.  What  is  the  least  value  of  x  +  y,  if  10 
 digit  number  780x533y24  is  divisible  by 
 88 ? 
 SSC CHSL 03/08/2023 (4th Shift) 
 (a) 4  (b) 3  (c) 1  (d) 2 
 Q.6.  During  a  division,  Pranjal  mistakenly 
 took  as  the  dividend  a  number  that  was 
 10%  more  than  the  original  dividend.  He 
 also  mistakenly  took  as  the  divisor  a 
 number  that  was  25%  more  than  the 
 original  divisor.  If  the  correct  quotient  of 
 the  original  division  problem  was  25  and 
 the  remainder  was  0,  what  was  the 
 quotient  that  Pranjal  obtained,  assuming 
 his calculations had no error ? 
 SSC CGL 17/07/2023 (4th shift) 
 (a) 21.75  (b) 21.25   (c) 28.75  (d) 22 
 Q.7.  The  six-digit  number  7x1yyx  is  a 
 multiple  of  33  for  non-zero  digits  x  and  y. 
 Which  of  the  following  could  be  a 
 possible value of (x + y) ? 
 Matriculation Level 30/06/2023 (Shift - 4) 
 (a) 5  (b) 4  (c) 2  (d) 3 
 Q.8.  A  girl  wants  to  plant  trees  in  her 
 garden  in  rows  in  such  a  way  that  the 
 number  of  trees  in  each  row  to  be  the 
 same.  There  are  10  rows  and  the  number 
 of  trees  in  each  row  is  12,  what  is  the 
 number  of  trees  in  each  row,  if  there  are 
 5 more rows ? 
 SSC MTS 17/05/2023 (Evening) 
 (a) 10  (b) 8  (c) 6  (d) 12 
 Q.9.  What  is  the  total  number  of  factors 
 of  the  number  720  except  1  and  the 
 number itself? 
 SSC CHSL 10/03/2023 (4th Shift) 
 (a) 29  (b) 27  (c) 32  (d) 28 
 Q.10.  Which  of  the  following  is  the 
 smallest  among  (  14  )  ,  (  12  )  ,  (  16  ) 
 1 
 3 
 1 
 2 
 1 
 6 
 & 
 (  25  )  ? 
 1 
 12 
 SSC CHSL 10/03/2023 (3rd Shift) 
 (a)  (  14  )  (b)  (  25  )  (c)  (  16  )  (d)  (  12  ) 
 1 
 3 
 1 
 12 
 1 
 6 
 1 
 2 
 Q.11.  Which  of  the  following  statements 
 is correct ? 
 I.The  Value  of  100 
 2 
 -  99 
 2 
 +  98 
 2 
 -  97 
 2 
 +  96 
 2 
 - 95 
 2 
 + 94 
 2 
 - 93 
 2 
 + ...... + 22 
 2 
 - 21 
 2 
 is 4840. 
 II. The value of  (  )  (  ) (  ?? 
 2 
+
 1 
 ?? 
 2 
 ?? -
 1 
 ?? 
 ?? 
 4 
 )(  )(  )  is K 
 16 
 - +
 1 
 ?? 
 4 
 ?? +
 1 
 ?? 
 ?? 
 4 
-
 1 
 ?? 
 4 
 1 
 ?? 
 16 
 SSC CGL 13/12/2022 (3rd Shift) 
 (a) Neither I nor II  (b) Both I and II 
 (c) Only II  (d) Only I 
 Q.12.  If  the  seven-digit  number  52A6B7C 
 is  divisible  by  33,  and  A,  B,  C  are  primes, 
 then the maximum value of 2A+3B+C is: 
 SSC CGL 12/12/2022 (3rd Shift) 
 (a) 32  (b) 23  (c) 27  (d) 34 
 Q.13.  If  the  9  -  digit  number  83P93678Q 
 is  divisible  by  72,  then  what  is  the  value 
 of  ?  ?? 
 2 
+ ?? 
 2 
+ 12    
 SSC CGL  05/12/2022 (4th Shift) 
 (a) 6  (b) 7  (c) 8  (d) 9 
 Q.14.  In  a  test  (+  5)  marks  are  given  for 
 every  correct  answer  and  (-2)  marks  are 
 given  for  every  incorrect  answer.  Jay 
 answered  all  the  questions  and  scored 
 (-12)  marks,  though  he  got  4  correct 
 answers.  How  many  of  his  answers  were 
 INCORRECT ? 
 SSC CPO 11/11/2022 (Evening) 
 (a) 8  (b) 32  (c) 16  (d) 20 
 Q.15.  What  is  the  sum  of  all  the  common 
 terms  between  the  given  series  S1  and 
 S2 ? 
 S1 = 2, 9, 16, ……., 632 
 S2 = 7, 11, 15, ……., 743 
 SSC CGL Tier II  (08/08/2022) 
 (a) 6974  (b) 6750   (c) 7140   (d) 6860 
 Q.16.  If  the  7  -  digit  number  x8942y4  is 
 divisible  by  56,  what  is  the  value  of  (  +  ?? 
 2 
 y)  for  the  largest  value  of  y,  where  x  and  y 
 are natural numbers? 
 SSC CGL 11/04/2022 (Evening) 
 (a) 33  (b) 44  (c) 55  (d) 70 
 Q.17.  Let p, q, r and s be positive natural 
 numbers having three exact factors 
 www.ssccglpinnacle.com                                                 Download Pinnacle Exam Preparation App 3
 Pinnacle  Day: 1st - 5th  Number System 
 including  1  and  the  number  itself  If  q  >  p 
 and  both  are  two-digit  numbers,  and  r  >  s 
 and  both  are  one-digit  numbers,  then  the 
 value of the expression  is: 
 ??    -    ??    -    1 
 ??    -    ?? 
 SSC CGL Tier II  (03/02/2022) 
 (a) - s - 1   (b) s - 1   (c) 1 - s   (d) s + 1 
 Q.18.  Three  fractions  x,  y  and  z  are  such 
 that  x  >  y  >  z.  When  the  smallest  of  them 
 is  divided  by  the  greatest,  the  result  is 
 which  exceeds  y  by  0.0625.  If  x  +  y  + 
 9 
 16 
 z = 2  , then what is the value of x + z ? 
 3 
 12 
 SSC CGL Tier II  (29/01/2022) 
 (a)  (b)  (c)  (d) 
 5 
 4 
 1 
 4 
 7 
 4 
 3 
 4 
 Q.19.  The  six-digit  number  537xy5  is 
 divisible by 125. How many such six - 
 digit numbers are there? 
 SSC CHSL 19/04/2021 (Morning) 
 (a) 4  (b) 2  (c) 3  (d) 5 
 Q.20.  How  many  numbers  between  400 
 and 700 are divisible by 5, 6 and 7 ? 
 SSC CPO 24/11/2020 (Evening) 
 (a) 2  (b) 5  (c) 10  (d) 20 
 Q.21.  Find the number of prime factors in 
 the product  . ( 30 )
 5 
× ( 24 )
 5 
 SSC CGL Tier II (18/11/2020) 
 (a) 45  (b) 35  (c) 10  (d) 30 
 Q.22.  Let  ab,  a  b,  is  a  2-digit  prime ?
 number  such  that  ba  is  also  a  prime 
 number. The sum of all such number is: 
 SSC CGL Tier  II (16/11/2020) 
 (a) 374  (b) 418  (c) 407  (d) 396 
 Q.23.  Given  that  2 
 20 
 +  1  is  completely 
 divisible  by  a  whole  number.  Which  of  the 
 following  is  completely  divisible  by  the 
 same number ? 
 SSC CHSL 16/10/2020 (Afternoon) 
 (a)  2 
 15 
 + 1  (b) 5  2 
 30 
×
 (c) 2 
 90 
 + 1  (d)  2 
 60 
 + 1 
 Q.24.  Which  of  the  following  numbers 
 will completely divide 7 
 81 
 + 7 
 82 
 + 7 
 83 
 ? 
 SSC CHSL  17/03/2020 (Morning) 
 (a) 399  (b) 389  (c) 387       (d) 397 
 Q.25.  When  a  positive  integer  is  divided 
 by  d,  the  remainder  is  15.  When  ten  times 
 of  the  same  number  is  divided  by  d,  the 
 remainder  is  6.  The  least  possible  value 
 of d is: 
 SSC CGL 05/03/2020 (Afternoon) 
 (a) 9  (b) 12  (c) 16  (d) 18 
 Q.26.  When  200  is  divided  by  a  positive 
 integer  x,  the  remainder  is  8.  How  many 
 values of x are there? 
 SSC CGL 03/03/2020 (Afternoon) 
 (a) 7  (b) 5  (c) 8  (d) 6 
 Q.27.  The number 1563241234351 is : 
 SSC CPO  13/12/2019 (Evening) 
 (a) divisible by both 3 and 11 
 (b) divisible by 11 but not by 3 
 (c) neither divisible by 3 nor by 11 
 (d) divisible by 3 but not by 11 
 Q.28.  How  many  natural  numbers  less 
 than  1000  are  divisible  by  5  or  7  but  NOT 
 by 35 ? 
 SSC CPO  11/12/2019 (Morning) 
 (a) 285  (b) 313  (c) 341  (d) 243 
 Q.29.  If  r  is  the  remainder  when  each  of 
 4749,  5601  and  7092  is  divided  by  the 
 greatest  possible  number  d  (  1),  then  > 
 the value of (d + r) will be: 
 SSC CPO  11/12/2019 (Morning) 
 (a) 276  (b) 271  (c) 298  (d) 282 
 Q.30.  Let  x  be  the  least  4-digit  number 
 which  when  divided  by  2,  3,  4,  5,  6  and  7 
 leaves  a  remainder  of  1  in  each  case.  If  x 
 lies  between  2800  and  3000,  then  what  is 
 the sum of digits of x ? 
 SSC CPO  09/12/2019 (Evening) 
 (a) 15  (b) 16  (c) 12  (d) 13 
 Q.31.  If  the  six  digit  number  479xyz  is 
 exactly  divisible  by  7,  11  and  13  ,  then  {(  y 
 + z ) ÷ x} is equal to : 
 SSC CPO  09/12/2019 (Morning) 
 (a)  (b) 4  (c)  (d) 
 11 
 9 
 13 
 7 
 7 
 13 
 Q.32.  Which  among  the  following  is  the 
 smallest? 
 SSC CPO 09/12/19 (Morning) 
 (a) v401 - v399     (b) v101 - v99 
 (c) v301 - v299     (d) v201 - v199 
 Q.33.  If  x  is  the  remainder  when  3 
 61284 
 is 
 divided  by  5  and  y  is  the  remainder  when 
 4 
 96 
 is  divided  by  6,  then  what  is  the  value 
 of (2x - y) ? 
 SSC CGL Tier II (13/09/2019) 
 (a) - 4  (b) 4        (c) -2  (d) 2 
 Q.34.  In  ?nding  the  HCF  of  two  numbers 
 by  division  method,  the  last  divisor  is  17 
 and  the  quotients  are  1,  11  and  2, 
 respectively.  What  is  the  sum  of  the  two 
 numbers ? 
 SSC CGL Tier II (13/09/2019) 
 (a) 833  (b) 867  (c) 816  (d) 901 
 Q.35.  Two  positive  numbers  differ  by 
 2001.  When  the  larger  number  is  divided 
 by  the  smaller  number,  the  quotient  is  9 
 and  the  remainder  is  41.  The  sum  of  the 
 digits of the larger number is : 
 SSC CGL Tier II (13/09/2019) 
 (a) 15  (b) 11  (c) 10  (d) 14 
 Q.36.  When  a  two-digit  number  is 
 multiplied  by  the  sum  of  its  digits,  the 
 product  is  424.  When  the  number 
 obtained  by  interchanging  its  digits  is 
 multiplied  by  the  sum  of  the  digits,  the 
 result  is  280.  The  sum  of  the  digits  of  the 
 given number is : 
 SSC CGL Tier II (12/09/2019) 
 (a) 6  (b) 9  (c) 8  (d) 7 
 Q.37.  Let  x  be  the  least  number  which 
 when  divided  by  15,18,20  and  27,  the 
 remainder  in  each  case  is  10  and  x  is  a 
 multiple  of  31.  What  least  number  should 
 be added to x to make it a perfect square ? 
 SSC CGL Tier II (12/09/2019) 
 (a) 39  (b) 37  (c) 43  (d) 36 
 Q.38.  The number of factors of 3600 is : 
 SSC CGL Tier II  (12/09/2019) 
 (a) 45  (b) 44  (c) 43  (d) 42 
 Q.39.  When  12,  16,  18,  20  and  25  divide 
 the  least  number  x,  the  remainder  in  each 
 case  is  4  but  x  is  divisible  by  7.  What  is 
 the digit at the thousands’ place in x ? 
 SSC CGL Tier II  (11/09/2019) 
 (a) 5  (b) 8  (c) 4  (d) 3 
 Q.40.  One  of  the  factors  of  (  ),  8 
 2  ?? 
+ 5 
 2  ?? 
 where k is an odd number, is : 
 SSC CGL Tier II (11/09/2019) 
 (a) 86  (b) 88  (c) 84  (d) 89 
 Q.41.  Let  x  = ( 633 )
 24 
- ( 277 )
 38 
+
 What is the unit digit of x ? ( 266 )
 54 
 SSC CGL Tier  II  (11/09/2019) 
 (a) 7  (b) 6  (c) 4  (d) 8 
 Q.42.  The  sum  of  the  digits  of  a  two-digit 
 number  is  of  the  number.  The  unit 
 1 
 7 
 digit  is  4  less  than  the  tens  digit.  If  the 
 number  obtained  on  reversing  its  digit  is 
 divided by 7, the remainder will be : 
 SSC CGL Tier  II  (11/09/2019) 
 (a) 4  (b) 5  (c) 1  (d) 6 
 Q.43.  When  6892,  7105  and  7531  are 
 divided  by  the  greatest  number  x,  then 
 the  remainder  in  each  case  is  y.  What  is 
 the value of (x - y) ? 
 SSC MTS 22/08/2019 (Afternoon) 
 (a) 123  (b) 137  (c) 147    (d) 113 
 Q.44.  Let  x  be  the  greatest  number  which 
 when  divides  6475,  4984  and  4132,  the 
 remainder  in  each  case  is  the  same. 
 What is the sum of digits of x? 
 SSC MTS 22/08/2019 (Morning) 
 (a) 4  (b) 7  (c) 5  (d) 6 
 Q.45.  When  an  integer  n  is  divided  by  8, 
 the  remainder  is  3.  What  will  be  the 
 remainder if 6n - 1 is divided by 8 ? 
 SSC CGL 13/06/2019 (Evening) 
 www.ssccglpinnacle.com                                                 Download Pinnacle Exam Preparation App 4
 Pinnacle  Day: 1st - 5th  Number System 
 (a) 4  (b) 1  (c) 0  (d) 2 
 Q.46.  If a 11 digit number 5y5884805x6 
 is  divisible  by  72,  where  x  =  y,  then  the 
 value of  is :  ???? 
 SSC CGL 10/06/2019 (Morning) 
 (a)  (b) 3  (c) 7  (d) 2  7  7 
 Q.47.  A  gardener  planted  1936  saplings 
 in  a  garden  such  that  there  were  as  many 
 rows  of  saplings  as  the  columns.  The 
 number of rows planted is : 
 SSC CPO 16/03/2019 (Afternoon) 
 (a) 46  (b) 44  (c) 48  (d)42 
 Q.48.  What  is  the  difference  between  the 
 largest  and  smallest  numbers  of  the  four 
 digits created using numbers 2, 9, 6, 5 ? 
 (Each number can be used only once) 
 SSC CPO 14/03/2019 (Evening) 
 (a) 6993    (b) 7056   (c) 6606    (d) 7083 
 Q.49.  The  sum  of  all  possible  three  digit 
 numbers  formed  by  digits  3,  0  and  7, 
 using each digit only once is: 
 SSC CPO 14/03/2019 (Morning) 
 (a) 2010    (b) 1990    (c) 2220     (d) 2110 
 Q.50.  What  is  the  sum  of  digits  of  the 
 least  number,  which  when  divided  by  15, 
 18  and  42  leaves  the  same  remainder  8 
 in each case and is also divisible by 13 ? 
 SSC CPO 13/03/2019 (Evening) 
 (a) 25  (b) 24  (c) 22  (d) 26 
 Q.51.  The  square  root  of  which  of  the 
 following is a rational number ? 
 SSC CPO 12/03/2019 (Morning) 
 (a) 1250.49  (b) 6250.49 
 (c) 1354.24  (d) 5768.28 
 Q.52.  What  is  the  sum  of  the  digits  of  the 
 least  number,  which  when  divided  by  12  , 
 16  and  54,  leaves  the  same  remainder  7 
 in  each  case  and  is  also  completely 
 divisible by 13 ? 
 SSC CPO 12/03/2019 (Evening) 
 (a) 36  (b) 16  (c) 9  (d) 27 
 Practice Questions 
 SSC CHSL 2023 Tier - 1 
 Q.53.  Which  of  the  following  is  the 
 nearest  number  to  13051  and  is  divisible 
 by 9 ? 
 SSC CHSL 02/08/2023 (3rd Shift) 
 (a) 13057 (b) 13056 (c) 13059 (d) 13058 
 Q.54.  A  Number  when  divided  by  78 
 gives  the  quotient  280  and  the  remainder 
 0.  If  the  same  number  is  divided  by  65, 
 what will be the value of the remainder ? 
 SSC CHSL 02/08/2023 (4th Shift) 
 (a) 1  (b) 3  (c) 0  (d) 2 
 Q.55.  The  divisor  is  10  times  the  quotient 
 and  5  times  the  remainder  in  a  division 
 sum.  What  is  the  dividend  if  the 
 remainder is 46 ? 
 SSC CHSL 03/08/2023 (2nd Shift) 
 (a) 5972  (b) 4286  (c) 4874  (d) 5336 
 Q.56.  What  is  the  largest  ?ve  digit 
 number exactly divisible by 88 ? 
 SSC CHSL 04/08/2023 (1st Shift) 
 (a) 99992 (b) 99986 (c) 99984 (d) 99968 
 Q.57.  What  is  the  least  number  that  must 
 be  added  to  the  greatest  6-digit  number 
 so  that  the  sum  will  be  exactly  divisible 
 by 294 ? 
 SSC CHSL 07/08/2023 (2nd Shift) 
 (a) 234  (b) 194  (c) 269  (d) 189 
 Q.58.  Which  of  the  following  sets  is  such 
 that  all  its  elements  are  divisors  of  the 
 number 2520 ? 
 SSC CHSL 08/08/2023 (1st Shift) 
 (a) 12, 49, 18  (b)  8 , 9, 7 
 (c) 16, 15, 14            (d) 21, 10, 25 
 Q.59.  What  is  the  remainder  when  3 
 8 
 is 
 divided by 7 ? 
 SSC CHSL 08/08/2023 (2nd Shift) 
 (a) 5  (b) 4  (c) 6  (d) 2 
 Q.60.  If  7  divides  the  integer  n,  then  the 
 remainder  is  2.  What  will  be  the 
 remainder if 9n is divided by 7 ? 
 SSC CHSL 09/08/2023 (1st Shift) 
 (a) 3  (b) 5  (c) 1  (d) 4 
 Q.61.  What  will  be  the  greatest  number 
 32a78b,  which  is  divisible  by  3  but  NOT 
 divisible  by  9  ?  (Where  a  and  b  are  single 
 digit numbers). 
 SSC CHSL 09/08/2023 (2nd Shift) 
 (a) 324781  (b) 329787 
 (c) 326787  (d) 329784 
 Q.62.  The  sum  of  the  cubes  of  two  given 
 numbers  is  10234,  while  the  sum  of  the 
 two  given  numbers  is  34.  What  is  the 
 positive  difference  between  the  cubes  of 
 the two given numbers ? 
 SSC CHSL 11/08/2023 (1st Shift) 
 (a) 3484   (b) 3488   (c) 3356   (d) 8602 
 Q.63.  If  a  10-digit  number  620x976y52  is 
 divisible  by  88,  then  the  least  value  of  (x² 
 + y²) will be: 
 SSC CHSL 14/08/2023 (3rd Shift) 
 (a) 8  (b) 7  (c) 11  (d) 10 
 Q.64.  The  six-digit  number  N  =  4a6b9c  is 
 divisible  by  99,  then  the  maximum  sum 
 of the digits of N is: 
 SSC CHSL 17/08/2023 (1st Shift) 
 (a) 18  (b) 36  (c) 45  (d) 27 
 SSC CGL 2023 Tier - 1 
 Q.65.  What  will  be  the  remainder  when 
 (265) 
 4081 
 + 9 is divided by 266 ? 
 SSC CGL 14/07/2023 (1st shift) 
 (a) 8  (b) 6  (c) 1  (d) 9 
 Q.66.  A  and  B  have  some  toffees.  If  A 
 gives  one  toffee  to  B,  then  they  have  an 
 equal  number  of  toffees.  If  B  gives  one 
 toffee  to  A,  then  the  toffees  with  A  are 
 double  with  B.  The  total  number  of 
 toffees with A and B are _______. 
 SSC CGL 14/07/2023 (3rd shift) 
 (a) 12  (b) 10  (c) 14  (d) 15 
 Q.67.  Find the smallest number that can 
 be subtracted from 148109326 so that it 
 becomes divisible by 8. 
 SSC CGL 17/07/2023 (1st shift) 
 (a) 4  (b) 8  (c) 6  (d) 10 
 Q.68.  The largest 5-digit number exactly 
 divisible by 88 is: 
 SSC CGL 17/07/2023 (2nd shift) 
 (a) 99990  (b) 99984  (c) 99978  (d) 99968 
 Q.69.  Find the sum of 3 + 3 
 2 
 + 3 
 3 
 + ……. + 3 
 8 
 . 
 SSC CGL 17/07/2023 (2nd shift) 
 (a) 6561  (b) 6560  (c) 9840  (d) 3280 
 Q.70.  How  many  of  the  following 
 numbers are divisible by 132 ? 
 660,  754,  924,  1452,  1526,  1980,  2045 
 and 2170 
 SSC CGL 17/07/2023 (3rd shift) 
 (a) 3  (b) 6  (c) 5  (d) 4 
 Q.71.  A  six  -  digit  number  is  divisible  by 
 33.  If  54  is  added  to  the  number,  then  the 
 new  number  formed  will  also  be  divisible 
 by : 
 SSC CGL 17/07/2023 (4th shift) 
 (a) 3  (b) 2  (c) 5  (d) 7 
 Q.72.  Which  of  the  following  numbers  is 
 divisible by 24 ? 
 SSC CGL 18/07/2023 (1st shift) 
 (a) 52668  (b) 49512  (c) 64760  (d) 26968 
 Q.73.  The  cost  of  32  pens  and  12  pencils 
 is  ?790.  What  is  the  total  cost  (in  ?  )  of  8 
 pens and 3 pencils together? 
 SSC CGL 18/07/2023 (2nd shift) 
 (a) 200.5  (b) 197.5  (c) 180.5  (d) 220.5 
 Q.74.  The  smallest  number  added  to  888 
 so that it is exactly divisible by 35 is : 
 SSC CGL 18/07/2023 (3rd shift) 
 (a) 22  (b) 23  (c) 20  (d) 21 
 Q.75.  An  11-digit  number  7823326867X 
 is divisible by 18. What is the value of X? 
 SSC CGL 19/07/2023 (1st shift) 
 (a) 6  (b) 4  (c) 8  (d) 2 
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FAQs on SSC CGL Previous Year Questions (2023-18): Number System - SSC CGL Previous Year Papers

1. What are the different types of numbers in the number system?
Ans. The number system includes various types of numbers such as natural numbers, whole numbers, integers, rational numbers, irrational numbers, and real numbers.
2. How can one determine if a number is prime or composite?
Ans. A number is considered prime if it has exactly two factors, 1 and itself. If a number has more than two factors, then it is classified as a composite number.
3. What is the significance of the concept of LCM and HCF in the number system?
Ans. The concept of Least Common Multiple (LCM) and Highest Common Factor (HCF) is crucial in simplifying fractions, solving word problems, and finding the common multiple or factor of two or more numbers.
4. How can one convert a decimal number to a fraction in the number system?
Ans. To convert a decimal number to a fraction, count the number of decimal places and put the decimal number over a power of 10 (e.g., 0.5 = 5/10 = 1/2).
5. How do you find the square root of a number in the number system?
Ans. To find the square root of a number, one can use the prime factorization method, long division method, or estimation method depending on the complexity of the number.
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shortcuts and tricks

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Summary

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Semester Notes

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Exam

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Previous Year Questions with Solutions

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video lectures

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study material

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