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RS Aggarwal Solutions: Exercise 11B - Compound Interest | Mathematics (Maths) Class 8 PDF Download

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 Page 1


B y u s i n g t h e f o r m u l a , f i n d t h e a m o u n t a n d c o m p o u n d i n t e r e s t o n :
( 1 ) R s 6 0 0 0 f o r 2 y e a r s a t 9 % p e r a n n u m c o m p o u n d e d a n n u a l l y .
Principal (P) =6000
Rate of the interest (R) = 9%
Time of the interest (N) = 2 years
Amount = P( 1+R/100)*n
Amount = 6000 (1+9/100)*2
Amount = 6000 (1.09)*2
Amount = 6000 (1.09×1.09)
Amount = 6000× 1.1881
Amount = Rupees 7128.60
Compounded Interest = Amount - Principal
C.I = 7128.6- 6000.0
C.I = 1128.6 
( 2 ) R s 1 0 0 0 0 f o r 2 y e a r s a t 1 1 % p e r a n n u m c o m p o u n d e d a n n u a l l y .
Given,
Principal=Rs. 10000
Rate =11%
Time =2 years
Compound=P(1+r100)2
=10000(1+11100)2
=10000×(111)210000
=12321
Amount=12321-10000=2321.
( 3 ) R s 3 1 2 5 0 f o r 3 y e a r s a t 8 % p e r a n n u m c o m p o u n d e d a n n u a l l y .
Page 2


B y u s i n g t h e f o r m u l a , f i n d t h e a m o u n t a n d c o m p o u n d i n t e r e s t o n :
( 1 ) R s 6 0 0 0 f o r 2 y e a r s a t 9 % p e r a n n u m c o m p o u n d e d a n n u a l l y .
Principal (P) =6000
Rate of the interest (R) = 9%
Time of the interest (N) = 2 years
Amount = P( 1+R/100)*n
Amount = 6000 (1+9/100)*2
Amount = 6000 (1.09)*2
Amount = 6000 (1.09×1.09)
Amount = 6000× 1.1881
Amount = Rupees 7128.60
Compounded Interest = Amount - Principal
C.I = 7128.6- 6000.0
C.I = 1128.6 
( 2 ) R s 1 0 0 0 0 f o r 2 y e a r s a t 1 1 % p e r a n n u m c o m p o u n d e d a n n u a l l y .
Given,
Principal=Rs. 10000
Rate =11%
Time =2 years
Compound=P(1+r100)2
=10000(1+11100)2
=10000×(111)210000
=12321
Amount=12321-10000=2321.
( 3 ) R s 3 1 2 5 0 f o r 3 y e a r s a t 8 % p e r a n n u m c o m p o u n d e d a n n u a l l y .
Given,
Principal=Rs. 31250
Rate r=8%
Time =3 years
Amount=p(1+r100)t
=31250(1+8100)3
=31250×(108100)3
=39,366Rs
compound=amount-principal
=39,366-31250
=Rs. 8116.
( 4 ) R s 1 0 2 4 0 f o r 3 y e a r s a t 1 2 ( 1 / 2 ) % p e r a n n u m c o m p o u n d e d a n n u a l l y .
Given p=Rs. 10240
r=1212% ?252%
Time=3 years
Amount=p(1+r100)t=10240(1+25/2100)3
=10240(1+18)3
=10240×(98)3
=14,580
Amount=14,580
( 5 ) R s 6 2 5 0 0 f o r 2 y e a r s 6 m o n t h s a t 1 2 % p e r a n n u m c o m p o u n d e d a n n u a l l y .
Solution
Principal (P)=Rs. 62500Rate (R)= 12% p.a.Period (n) = 2 years 6 months= 212 years
Here for first 2 years, we apply the compound interest formula and next 6 months, we apply
simple interest formula.
The amount for 2 years is
Page 3


B y u s i n g t h e f o r m u l a , f i n d t h e a m o u n t a n d c o m p o u n d i n t e r e s t o n :
( 1 ) R s 6 0 0 0 f o r 2 y e a r s a t 9 % p e r a n n u m c o m p o u n d e d a n n u a l l y .
Principal (P) =6000
Rate of the interest (R) = 9%
Time of the interest (N) = 2 years
Amount = P( 1+R/100)*n
Amount = 6000 (1+9/100)*2
Amount = 6000 (1.09)*2
Amount = 6000 (1.09×1.09)
Amount = 6000× 1.1881
Amount = Rupees 7128.60
Compounded Interest = Amount - Principal
C.I = 7128.6- 6000.0
C.I = 1128.6 
( 2 ) R s 1 0 0 0 0 f o r 2 y e a r s a t 1 1 % p e r a n n u m c o m p o u n d e d a n n u a l l y .
Given,
Principal=Rs. 10000
Rate =11%
Time =2 years
Compound=P(1+r100)2
=10000(1+11100)2
=10000×(111)210000
=12321
Amount=12321-10000=2321.
( 3 ) R s 3 1 2 5 0 f o r 3 y e a r s a t 8 % p e r a n n u m c o m p o u n d e d a n n u a l l y .
Given,
Principal=Rs. 31250
Rate r=8%
Time =3 years
Amount=p(1+r100)t
=31250(1+8100)3
=31250×(108100)3
=39,366Rs
compound=amount-principal
=39,366-31250
=Rs. 8116.
( 4 ) R s 1 0 2 4 0 f o r 3 y e a r s a t 1 2 ( 1 / 2 ) % p e r a n n u m c o m p o u n d e d a n n u a l l y .
Given p=Rs. 10240
r=1212% ?252%
Time=3 years
Amount=p(1+r100)t=10240(1+25/2100)3
=10240(1+18)3
=10240×(98)3
=14,580
Amount=14,580
( 5 ) R s 6 2 5 0 0 f o r 2 y e a r s 6 m o n t h s a t 1 2 % p e r a n n u m c o m p o u n d e d a n n u a l l y .
Solution
Principal (P)=Rs. 62500Rate (R)= 12% p.a.Period (n) = 2 years 6 months= 212 years
Here for first 2 years, we apply the compound interest formula and next 6 months, we apply
simple interest formula.
The amount for 2 years is
? Amount (A)=P (1+R100)n=Rs. 62500 (1+12100)2=Rs. 62500×(2825)2×5350=Rs.
62500×2825×2825100×784=Rs. 78400
The amount for next 6 months: 78400×(1+12×1100×2)
=78400×5350
=83104
Therefore, amount after 212 years is Rs. 83104
? C.I = A- P=Rs. 83104-Rs. 62500=Rs. 20604
( 6 ) R s 9 0 0 0 f o r 2 y e a r s 4 m o n t h s a t 1 0 % p e r a n n u m c o m p o u n d e d a n n u a l l y .
Solution
Given: Principal (P)=Rs. 9000
Rate (R)=10% per annum
Time (n)=2 years 4 months
=213 years [ ?1 year =12 months]
Amount for 2 years
? Amount (A)=P(1+R100)n
=Rs. 9000 (1+10100)2
=Rs. 9000×1110×1110
=Rs. 10890
For the next 13 years, Principal = Amount for 2 years =Rs. 10890.
Interest for 13 years =P×R×n100
=(10890×10×13100)
=Rs. 363
So, the total Amount for 213 years =Rs. 10890+363=Rs. 11253
?C.I.=A-P=Rs. 11253-Rs.9000
=Rs. 2253
Page 4


B y u s i n g t h e f o r m u l a , f i n d t h e a m o u n t a n d c o m p o u n d i n t e r e s t o n :
( 1 ) R s 6 0 0 0 f o r 2 y e a r s a t 9 % p e r a n n u m c o m p o u n d e d a n n u a l l y .
Principal (P) =6000
Rate of the interest (R) = 9%
Time of the interest (N) = 2 years
Amount = P( 1+R/100)*n
Amount = 6000 (1+9/100)*2
Amount = 6000 (1.09)*2
Amount = 6000 (1.09×1.09)
Amount = 6000× 1.1881
Amount = Rupees 7128.60
Compounded Interest = Amount - Principal
C.I = 7128.6- 6000.0
C.I = 1128.6 
( 2 ) R s 1 0 0 0 0 f o r 2 y e a r s a t 1 1 % p e r a n n u m c o m p o u n d e d a n n u a l l y .
Given,
Principal=Rs. 10000
Rate =11%
Time =2 years
Compound=P(1+r100)2
=10000(1+11100)2
=10000×(111)210000
=12321
Amount=12321-10000=2321.
( 3 ) R s 3 1 2 5 0 f o r 3 y e a r s a t 8 % p e r a n n u m c o m p o u n d e d a n n u a l l y .
Given,
Principal=Rs. 31250
Rate r=8%
Time =3 years
Amount=p(1+r100)t
=31250(1+8100)3
=31250×(108100)3
=39,366Rs
compound=amount-principal
=39,366-31250
=Rs. 8116.
( 4 ) R s 1 0 2 4 0 f o r 3 y e a r s a t 1 2 ( 1 / 2 ) % p e r a n n u m c o m p o u n d e d a n n u a l l y .
Given p=Rs. 10240
r=1212% ?252%
Time=3 years
Amount=p(1+r100)t=10240(1+25/2100)3
=10240(1+18)3
=10240×(98)3
=14,580
Amount=14,580
( 5 ) R s 6 2 5 0 0 f o r 2 y e a r s 6 m o n t h s a t 1 2 % p e r a n n u m c o m p o u n d e d a n n u a l l y .
Solution
Principal (P)=Rs. 62500Rate (R)= 12% p.a.Period (n) = 2 years 6 months= 212 years
Here for first 2 years, we apply the compound interest formula and next 6 months, we apply
simple interest formula.
The amount for 2 years is
? Amount (A)=P (1+R100)n=Rs. 62500 (1+12100)2=Rs. 62500×(2825)2×5350=Rs.
62500×2825×2825100×784=Rs. 78400
The amount for next 6 months: 78400×(1+12×1100×2)
=78400×5350
=83104
Therefore, amount after 212 years is Rs. 83104
? C.I = A- P=Rs. 83104-Rs. 62500=Rs. 20604
( 6 ) R s 9 0 0 0 f o r 2 y e a r s 4 m o n t h s a t 1 0 % p e r a n n u m c o m p o u n d e d a n n u a l l y .
Solution
Given: Principal (P)=Rs. 9000
Rate (R)=10% per annum
Time (n)=2 years 4 months
=213 years [ ?1 year =12 months]
Amount for 2 years
? Amount (A)=P(1+R100)n
=Rs. 9000 (1+10100)2
=Rs. 9000×1110×1110
=Rs. 10890
For the next 13 years, Principal = Amount for 2 years =Rs. 10890.
Interest for 13 years =P×R×n100
=(10890×10×13100)
=Rs. 363
So, the total Amount for 213 years =Rs. 10890+363=Rs. 11253
?C.I.=A-P=Rs. 11253-Rs.9000
=Rs. 2253
( 7 ) F i n d t h e a m o u n t o f R s 8 0 0 0 f o r 2 y e a r s c o m p o u n d e d a n n u a l l y a n d t h e r a t e s b e i n g 9 %
p e r a n n u m d u r i n g t h e f i r s t y e a r a n d 1 0 % p e r a n n u m d u r i n g t h e s e c o n d y e a r .
Solution
Principal (P) = Rs. 8000 Period
(n) = 2 years Rate (R1)=9% for the first year R2=10% the second year
? Amount (A)= P (1+R1100)1(1+R2100)1=8000 (1+9100) (1+10100)
=Rs 8000×109100×110100=Rs. 9592
( 8 ) A n a n d o b t a i n e d a l o a n o f R s 1 2 5 0 0 0 f r o m t h e A l l a h a b a d B a n k f o r b u y i n g c o m p u t e r s .
T h e b a n k c h a r g e s c o m p o u n d i n t e r e s t a t 8 % p e r a n n u m , c o m p o u n d e d a n n u a l l y . W h a t
a m o u n t w i l l h e h a v e t o p a y a f t e r 3 y e a r s t o c l e a r t h e d e b t ?
Solution
Principal (p) = 1,25,000
Rate of interest (r) = 8% p.a.
Period (n) = 3 years
? Amount (A) = P(1+r100)n
=Rs. 125000×(1+8100)3
=Rs. 125000×(2725)3
=Rs. 125000×2725×2725×2725
=Rs. 157464 Ans.
( 9 ) T h r e e y e a r s a g o , B e e r u p u r c h a s e d a b u f f a l o f r o m S u r j e e t f o r R s 1 1 0 0 0 . W h a t p a y m e n t
w i l l d i s c h a r g e h i s d e b t n o w , t h e r a t e o f i n t e r e s t b e i n g 1 0 % p e r a n n u m , c o m p o u n d e d
a n n u a l l y ?
Solution
Price of a buffalo (P) = Rs. 11000
Rate of interest (R)= 10% p.a.
Page 5


B y u s i n g t h e f o r m u l a , f i n d t h e a m o u n t a n d c o m p o u n d i n t e r e s t o n :
( 1 ) R s 6 0 0 0 f o r 2 y e a r s a t 9 % p e r a n n u m c o m p o u n d e d a n n u a l l y .
Principal (P) =6000
Rate of the interest (R) = 9%
Time of the interest (N) = 2 years
Amount = P( 1+R/100)*n
Amount = 6000 (1+9/100)*2
Amount = 6000 (1.09)*2
Amount = 6000 (1.09×1.09)
Amount = 6000× 1.1881
Amount = Rupees 7128.60
Compounded Interest = Amount - Principal
C.I = 7128.6- 6000.0
C.I = 1128.6 
( 2 ) R s 1 0 0 0 0 f o r 2 y e a r s a t 1 1 % p e r a n n u m c o m p o u n d e d a n n u a l l y .
Given,
Principal=Rs. 10000
Rate =11%
Time =2 years
Compound=P(1+r100)2
=10000(1+11100)2
=10000×(111)210000
=12321
Amount=12321-10000=2321.
( 3 ) R s 3 1 2 5 0 f o r 3 y e a r s a t 8 % p e r a n n u m c o m p o u n d e d a n n u a l l y .
Given,
Principal=Rs. 31250
Rate r=8%
Time =3 years
Amount=p(1+r100)t
=31250(1+8100)3
=31250×(108100)3
=39,366Rs
compound=amount-principal
=39,366-31250
=Rs. 8116.
( 4 ) R s 1 0 2 4 0 f o r 3 y e a r s a t 1 2 ( 1 / 2 ) % p e r a n n u m c o m p o u n d e d a n n u a l l y .
Given p=Rs. 10240
r=1212% ?252%
Time=3 years
Amount=p(1+r100)t=10240(1+25/2100)3
=10240(1+18)3
=10240×(98)3
=14,580
Amount=14,580
( 5 ) R s 6 2 5 0 0 f o r 2 y e a r s 6 m o n t h s a t 1 2 % p e r a n n u m c o m p o u n d e d a n n u a l l y .
Solution
Principal (P)=Rs. 62500Rate (R)= 12% p.a.Period (n) = 2 years 6 months= 212 years
Here for first 2 years, we apply the compound interest formula and next 6 months, we apply
simple interest formula.
The amount for 2 years is
? Amount (A)=P (1+R100)n=Rs. 62500 (1+12100)2=Rs. 62500×(2825)2×5350=Rs.
62500×2825×2825100×784=Rs. 78400
The amount for next 6 months: 78400×(1+12×1100×2)
=78400×5350
=83104
Therefore, amount after 212 years is Rs. 83104
? C.I = A- P=Rs. 83104-Rs. 62500=Rs. 20604
( 6 ) R s 9 0 0 0 f o r 2 y e a r s 4 m o n t h s a t 1 0 % p e r a n n u m c o m p o u n d e d a n n u a l l y .
Solution
Given: Principal (P)=Rs. 9000
Rate (R)=10% per annum
Time (n)=2 years 4 months
=213 years [ ?1 year =12 months]
Amount for 2 years
? Amount (A)=P(1+R100)n
=Rs. 9000 (1+10100)2
=Rs. 9000×1110×1110
=Rs. 10890
For the next 13 years, Principal = Amount for 2 years =Rs. 10890.
Interest for 13 years =P×R×n100
=(10890×10×13100)
=Rs. 363
So, the total Amount for 213 years =Rs. 10890+363=Rs. 11253
?C.I.=A-P=Rs. 11253-Rs.9000
=Rs. 2253
( 7 ) F i n d t h e a m o u n t o f R s 8 0 0 0 f o r 2 y e a r s c o m p o u n d e d a n n u a l l y a n d t h e r a t e s b e i n g 9 %
p e r a n n u m d u r i n g t h e f i r s t y e a r a n d 1 0 % p e r a n n u m d u r i n g t h e s e c o n d y e a r .
Solution
Principal (P) = Rs. 8000 Period
(n) = 2 years Rate (R1)=9% for the first year R2=10% the second year
? Amount (A)= P (1+R1100)1(1+R2100)1=8000 (1+9100) (1+10100)
=Rs 8000×109100×110100=Rs. 9592
( 8 ) A n a n d o b t a i n e d a l o a n o f R s 1 2 5 0 0 0 f r o m t h e A l l a h a b a d B a n k f o r b u y i n g c o m p u t e r s .
T h e b a n k c h a r g e s c o m p o u n d i n t e r e s t a t 8 % p e r a n n u m , c o m p o u n d e d a n n u a l l y . W h a t
a m o u n t w i l l h e h a v e t o p a y a f t e r 3 y e a r s t o c l e a r t h e d e b t ?
Solution
Principal (p) = 1,25,000
Rate of interest (r) = 8% p.a.
Period (n) = 3 years
? Amount (A) = P(1+r100)n
=Rs. 125000×(1+8100)3
=Rs. 125000×(2725)3
=Rs. 125000×2725×2725×2725
=Rs. 157464 Ans.
( 9 ) T h r e e y e a r s a g o , B e e r u p u r c h a s e d a b u f f a l o f r o m S u r j e e t f o r R s 1 1 0 0 0 . W h a t p a y m e n t
w i l l d i s c h a r g e h i s d e b t n o w , t h e r a t e o f i n t e r e s t b e i n g 1 0 % p e r a n n u m , c o m p o u n d e d
a n n u a l l y ?
Solution
Price of a buffalo (P) = Rs. 11000
Rate of interest (R)= 10% p.a.
Period (n) = 3 years
? Price of buffalo at present
(A)=(1+R100)n=Rs. 11000(1+10100)3=Rs. 11000×(1110)3
=Rs. 11000×1110×1110×1110
=Rs. 14641
( 1 0 ) S h u b h a l a x m i t o o k a l o a n o f R s 1 8 0 0 0 f r o m S u r y a F i n a n c e t o p u r c h a s e a T V s e t . I f t h e
c o m p a n y c h a r g e s i n t e r e s t a t 1 2 % p e r a n n u m d u r i n g t h e f i r s t y e a r a n d 1 2 ( 1 / 2 ) % p e r
a n n u m d u r i n g t h e s e c o n d y e a r , h o w m u c h w i l l s h e h a v e t o p a y a f t e r 2 y e a r s ?
S o l u t i o n :
Amount of loan taken (P) = Rs. 18000
Rate (R1)=12% p.a. during first yearR1=1212% = 252% p.a. during second year
Period (n) = 2 years
? Total amount (A)= P (1+R1100)1 (1+R2100)1= Rs. 18000 (1+12100) (1+252×100)= Rs.
18000×2825×98=Rs. 22680
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