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All questions of Series for UPSC CSE Exam
Look at this series: 8, 6, 9, 23, 87 , ... What number should come next?- a)128
- b)226
- c)324
- d)429
Correct answer is 'D'. Can you explain this answer?
a)
128
b)
226
c)
324
d)
429
|
Meghana Kaur answered |
8 x 1 - 2 = 6
6 x 2 - 3 = 9
9 x 3 - 4 = 23
23 x 4 - 5 = 87
87 x 5 - 6 = 429
6 x 2 - 3 = 9
9 x 3 - 4 = 23
23 x 4 - 5 = 87
87 x 5 - 6 = 429
Look at this series: 4, 9, 19, 39, 79,... What number should come next?- a)169
- b)159
- c)119
- d)139
Correct answer is option 'B'. Can you explain this answer?
a)
169
b)
159
c)
119
d)
139
|
Anjali Gupta answered |
The pattern is
4*2+1=9
9*2+1=19
19*2+1=39
39*2+1=79
79*2+1=159
4*2+1=9
9*2+1=19
19*2+1=39
39*2+1=79
79*2+1=159
Look at this series: 2, 6, 18, 54, ... What number should come next?- a)108
- b)148
- c)162
- d)216
Correct answer is option 'C'. Can you explain this answer?
a)
108
b)
148
c)
162
d)
216
|
|
Aisha Gupta answered |
CORRECT OPTION IS (C)
This is a simple multiplication series. Each number is 3 times more than the previous number.
This is a simple multiplication series. Each number is 3 times more than the previous number.
Find the missing number.
17, 19, 23, 29, 31, 37, _____
- a)47
- b)43
- c)40
- d)41
Correct answer is option 'D'. Can you explain this answer?
Find the missing number.
17, 19, 23, 29, 31, 37, _____
a)
47
b)
43
c)
40
d)
41
|
Shruti Dey answered |
The given numbers are consecutive prime numbers in increasing order starting with 17.
Hence, the next number in the series is 41.
Hence, the next number in the series is 41.
Look at this series: 201, 202, 204, 207, ... What number should come next?- a)205
- b)208
- c)210
- d)211
Correct answer is option 'D'. Can you explain this answer?
a)
205
b)
208
c)
210
d)
211
|
Nandini Iyer answered |
In this addition series, 1 is added to the first number; 2 is added to the second number; 3 is added to the third number; 4 is added to the fourth number; and go on.
0, 4, 18, 48, ___, 180- a)58
- b)144
- c)84
- d)100
Correct answer is option 'D'. Can you explain this answer?
0, 4, 18, 48, ___, 180
a)
58
b)
144
c)
84
d)
100
|
Lavanya Menon answered |
1st term = 5
2nd term = 5 × 2 + 3 = 13
3rd term = 13 × 3 + 2 = 41
4th term = 41 × 2 + 3 = 85
5th term = 85 × 3 + 2 =257...
2nd term = 5 × 2 + 3 = 13
3rd term = 13 × 3 + 2 = 41
4th term = 41 × 2 + 3 = 85
5th term = 85 × 3 + 2 =257...
⇒ For every term at even position, the previous term is multiplied by 2 and 3 is added.
⇒ For every term at odd position, the previous term is multiplied by 3 and 2 is added.
⇒ For every term at odd position, the previous term is multiplied by 3 and 2 is added.
So the missing term is: 257 × 2 + 3 = 517
Look at this series: 5.2, 4.8, 4.4, 4, ... What number should come next?- a)3
- b)3.3
- c)3.5
- d)3.6
Correct answer is option 'D'. Can you explain this answer?
a)
3
b)
3.3
c)
3.5
d)
3.6
|
Rajat Patel answered |
In this simple subtraction series, each number decreases by 0.4.
Look at this series: 14, 28, 20, 40, 32, 64, ... What number should come next?- a)52
- b)56
- c)92
- d)128
Correct answer is option 'B'. Can you explain this answer?
a)
52
b)
56
c)
92
d)
128
|
|
Anjali Gupta answered |
The series is 14, 28, 20, 40, 32, 64
Take three terms at a time. The notation be as follows:-
Let, First term = a = 14
It is evident that Second term= 2*a = 2 * 14 = 28 and,
The Third term = Second term - 8 OR ( 2*a - 8 ) = 28 - 8 = 20
Now consider the third, fourth and the fifth term.
Let, Third term = a = 20
It is evident that Fourth term= 2*a = 2 * 20 = 40 and,
The Fifth term = Second term - 8 OR ( 2*a - 8 ) = 40 - 8 = 32
Similarly consider fifth, sixth and the seventh(term to be found).
Let, Fifth term = a = 32
It is evident that Sixth term = 2*a = 2 * 32 = 64 and,
The Seventh term ( term to calculated) = Second term - 8 OR ( 2*a - 8 ) = 64 - 8 = 56
Take three terms at a time. The notation be as follows:-
Let, First term = a = 14
It is evident that Second term= 2*a = 2 * 14 = 28 and,
The Third term = Second term - 8 OR ( 2*a - 8 ) = 28 - 8 = 20
Now consider the third, fourth and the fifth term.
Let, Third term = a = 20
It is evident that Fourth term= 2*a = 2 * 20 = 40 and,
The Fifth term = Second term - 8 OR ( 2*a - 8 ) = 40 - 8 = 32
Similarly consider fifth, sixth and the seventh(term to be found).
Let, Fifth term = a = 32
It is evident that Sixth term = 2*a = 2 * 32 = 64 and,
The Seventh term ( term to calculated) = Second term - 8 OR ( 2*a - 8 ) = 64 - 8 = 56
17, __, 65, 113, 129, 161, 209.- a)34
- b)33
- c)40
- d)44
Correct answer is option 'B'. Can you explain this answer?
17, __, 65, 113, 129, 161, 209.
a)
34
b)
33
c)
40
d)
44
|
Shalini Patel answered |
1st term = 8
2nd term = 8 x 2 = 16
3rd term = 16 x 3 = 48
4th term = 48 x 2 = 96
5th term = 96 x 3 = 288
6th term = 288 x 2 = 576...
2nd term = 8 x 2 = 16
3rd term = 16 x 3 = 48
4th term = 48 x 2 = 96
5th term = 96 x 3 = 288
6th term = 288 x 2 = 576...
⇒ For every term at even position, the previous term is multiplied by 2.
⇒ For every term at odd position, the previous term is multiplied by 3.
⇒ For every term at odd position, the previous term is multiplied by 3.
So the missing term is: 576 × 3 = 1728
Look at this series: 544, 509, 474, 439, ... What number should come next?- a)404
- b)414
- c)420
- d)445
Correct answer is option 'A'. Can you explain this answer?
a)
404
b)
414
c)
420
d)
445
|
Bijoy Pillai answered |
Your answer is Option A: 404
In each number, you decrease 35, thus 404 is the right answer.
97, 83, 73, 67, 59, _____
- a)47
- b)49
- c)52
- d)53
Correct answer is option 'D'. Can you explain this answer?
97, 83, 73, 67, 59, _____
a)
47
b)
49
c)
52
d)
53
|
|
Aditya Kumar answered |
List of Prime Numbers from 1 to 100:
2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97,...
2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97,...
The given numbers are alternate prime numbers in decreasing order, starting with 97.
Hence, the next number in the series is 47.
12000, 2395, 474, 89.8, ___.- a)17.96
- b)12.96
- c)22.96
- d)none of these
Correct answer is option 'B'. Can you explain this answer?
12000, 2395, 474, 89.8, ___.
a)
17.96
b)
12.96
c)
22.96
d)
none of these
|
Vikas Kapoor answered |
The given numbers are squares of consecutive natural numbers in decreasing order starting with 15,
i.e., the numbers 225, 196, 169, ____, 100, 81 can be written as 152, 142, 132 , ____, 112 , 102 , 92.
i.e., the numbers 225, 196, 169, ____, 100, 81 can be written as 152, 142, 132 , ____, 112 , 102 , 92.
Hence, the missing number is 122 = 144.
Look at this series: 2, 4, 6, 8, 10, ... What number should come next?- a)11
- b)12
- c)13
- d)14
Correct answer is option 'B'. Can you explain this answer?
Look at this series: 2, 4, 6, 8, 10, ... What number should come next?
a)
11
b)
12
c)
13
d)
14
|
|
Kiran Reddy answered |
Each number increases by 2.
Like -
First number is 2
Second number = 2 + 2 =4
Third number = 4 + 2 = 6
Fourth number = 6 + 2 = 8
Fifth number = 8 + 2 = 10 and
Sixth number = 10 + 2 = 12
Hence, The answer is (b) 12.
Like -
First number is 2
Second number = 2 + 2 =4
Third number = 4 + 2 = 6
Fourth number = 6 + 2 = 8
Fifth number = 8 + 2 = 10 and
Sixth number = 10 + 2 = 12
Hence, The answer is (b) 12.
Look at this series: 1.5, 2.3, 3.1, 3.9, ... What number should come next?- a)4.2
- b)4.4
- c)4.7
- d)5.1
Correct answer is option 'C'. Can you explain this answer?
a)
4.2
b)
4.4
c)
4.7
d)
5.1
|
|
Alok Mehta answered |
In this simple addition series, each number increases by 0.8.
Rule = (1st no.) (1st no. + 0.8 = 2nd no.) (2nd no. + 0.8 = 3rd number)...
Now (1.5) (1.5 + 0.8 = 2.3) (2.3 + 0.8 = 3.1) (3.1 + 0.8 = 3.9) (3.9 + 0.8 = 4.7)...
So the anwser is c = 4.7
1, 8, 28, 99, 412, 2075, ____.- a)12450
- b)12462
- c)10387
- d)10375
Correct answer is option 'B'. Can you explain this answer?
1, 8, 28, 99, 412, 2075, ____.
a)
12450
b)
12462
c)
10387
d)
10375
|
|
Lavanya Menon answered |
The 1st to 5th terms are 0, 5, 22, 57, 116.
These terms are 1 – 1, 8 – 3, 27 – 5, 64 – 7, 125 – 9.
i.e. 13 – 1, 23 – 3, 33 – 5, 43 – 7, 53 – 9
These terms are 1 – 1, 8 – 3, 27 – 5, 64 – 7, 125 – 9.
i.e. 13 – 1, 23 – 3, 33 – 5, 43 – 7, 53 – 9
So, the nth term of the series: n3 – (2n – 1).
So, the 6th term of the series is 63 – (2 × 6 –1) = 216 – 11 = 205.
100, 70, 46, 28, __, 10- a)17
- b)15
- c)20
- d)16
Correct answer is option 'D'. Can you explain this answer?
100, 70, 46, 28, __, 10
a)
17
b)
15
c)
20
d)
16
|
|
Vivek Patel answered |
1st term = 75
2nd term = 75 + 216 = 75 + 63 = 291
3rd term = 291 + 125 = 291 + 53 = 416
4th term = 416 + 64 = 416 + 43 = 480
5th term = 480 + 27 = 480 + 33 = 507...
2nd term = 75 + 216 = 75 + 63 = 291
3rd term = 291 + 125 = 291 + 53 = 416
4th term = 416 + 64 = 416 + 43 = 480
5th term = 480 + 27 = 480 + 33 = 507...
The differences are cubes of consecutive natural numbers in decreasing order from 6.
So, the missing term = 507 + 8 = 507 + 23 = 515
So, the missing term = 507 + 8 = 507 + 23 = 515
Look at this series: 80, 10, 70, 15, 60, ... What number should come next?- a)20
- b)25
- c)30
- d)50
Correct answer is 'A'. Can you explain this answer?
a)
20
b)
25
c)
30
d)
50
|
|
Varun Kapoor answered |
This is an alternating addition and subtraction series. In the first pattern, 10 is subtracted from each number to arrive at the next. In the second, 5 is added to each number to arrive at the next.
7, 9, 13, 21, 37, ____- a)58
- b)63
- c)69
- d)72
Correct answer is option 'C'. Can you explain this answer?
7, 9, 13, 21, 37, ____
a)
58
b)
63
c)
69
d)
72
|
|
Lavanya Menon answered |
The common difference between consecutive terms is 6, 12, 6, 12 & so on. So, the term next to 141 is 141 + 6 = 147
1, 2, 8, 33, 148, __.- a)265
- b)465
- c)565
- d)765
Correct answer is option 'D'. Can you explain this answer?
1, 2, 8, 33, 148, __.
a)
265
b)
465
c)
565
d)
765
|
Ankit Saini answered |
1*1 + (1)2 = 1+1 = 2
2*2 + (2)2 = 4+4 = 8
8*3 + (3)2 = 24+9 = 33
33*4 + (4)2 = 132+16 = 148
148*5 + (5)2 =740+25 = 765
2*2 + (2)2 = 4+4 = 8
8*3 + (3)2 = 24+9 = 33
33*4 + (4)2 = 132+16 = 148
148*5 + (5)2 =740+25 = 765
8, 24, 12, ___, 18, 54- a)28
- b)36
- c)46
- d)38
Correct answer is option 'B'. Can you explain this answer?
8, 24, 12, ___, 18, 54
a)
28
b)
36
c)
46
d)
38
|
Abhiram Mehta answered |
So, term is 12*3 = 36.
Chapter doubts & questions for Series - CSAT Preparation 2025 is part of UPSC CSE exam preparation. The chapters have been prepared according to the UPSC CSE exam syllabus. The Chapter doubts & questions, notes, tests & MCQs are made for UPSC CSE 2025 Exam. Find important definitions, questions, notes, meanings, examples, exercises, MCQs and online tests here.
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