Compound Interest Questions

FACTS  AND  FORMULAE  FOR  COMPOUND  INTEREST  QUESTIONS

 

 

Let Principal = P, Rate = R% per annum, Time = n years.

I.

1.  When interest is compound Annually:

Amount =P1+R100n

2.  When interest is compounded Half-yearly:

Amount = P1+(R2)1002n

3.  When interest is compounded Quarterly:

Amount = P1+R41004n

 

II.

1.  When interest is compounded Annually but time is in fraction, say 325 years.

Amount = P1+R1003×1+25R100

2.  When Rates are different for different years, say R1%, R2%, R3% for 1st, 2nd and 3rd year respectively.

Then, Amount = P1+R11001+R21001+R3100

 

III.  Present worth of Rs. x due n years hence is given by:

Present Worth = x1+R100n

Q:

The difference between the compound interest and simple interest on a certain sum at 10% per annum for 2 years is Rs. 631. Find the sum.

A) 60100 B) 61100
C) 62100 D) 63100
 
Answer & Explanation Answer: D) 63100

Explanation:

Let the sum be Rs. x. Then,
C.I. = x ( 1 + ( 10 /100 ))^2 - x = 21x / 100 ,
S.I. = (( x * 10 * 2) / 100) = x / 5
(C.I) - (S.I) = ((21x / 100 ) - (x / 5 )) = x / 100
( x / 100 ) = 632 * x = 63100.
Hence, the sum is Rs.63,100.

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27 25088
Q:

The principal that amounts to Rs.4913 in 3 years at 413% per annum compound interest compounded annually is

A) Rs.3096 B) Rs.4076
C) Rs.4085 D) Rs.4096
 
Answer & Explanation Answer: D) Rs.4096

Explanation:

principal = A=4913,T=3, R=413

P=A1+R100T

 

 = Rs.4096

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30 24567
Q:

A man invests Rs.5000 for 3 years at 5% p.a. compound interest reckoned yearly. Income tax at the rate of 20% on the interest earned is deducted at the end of each year. Find the amount at the end of the third year

A) Rs.5624.32 B) Rs.5423
C) Rs.5634 D) Rs.5976
 
Answer & Explanation Answer: A) Rs.5624.32

Explanation:

 

 

 

5% is the rate of interest. 20% of the interest amount is paid as tax.

 

i.e  80% of the interest amount stays back.

 

 if we compute the rate of interest as 80% of 5% = 4% p.a., we will get the same value.

  

The interest accrued for 3 years in compound interest = 3 x simple interest on principal + 3 x interest on simple interest + 1 x interest on interest on interest.

 

= 3 x (200) + 3 x (8) + 1 x 0.32 =600 + 24 + 0.32 = 624.32

 

 

 

The amount at the end of 3 years = 5000 + 624.32 = 5624.32

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26 24285
Q:

The present worth of Rs.169 due in 2 years at 4% per annum compound interest is

A) Rs.156.25 B) Rs.150
C) Rs.140 D) Rs125.25
 
Answer & Explanation Answer: A) Rs.156.25

Explanation:

 

Present Worth

 

=P1+R1002

 

=1691+41002

 

= Rs.156.25

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30 24196
Q:

Rs. 5887 is divided between Shyam and Ram, such that Shyam's share at the end of 9 years is equal to Ram's share at the end of 11 years, compounded annually at the rate of 5%. Find the share of Shyam.

A) 3567 B) 3452
C) 3087 D) 3544
 
Answer & Explanation Answer: C) 3087

Explanation:

Shyam's share * (1+0.05)9 = Ram's share * (1 + 0.05)11

Shyam's share / Ram's share = (1 + 0.05)11 / (1+ 0.05)9 = (1+ 0.05)2 = 441/400

Therefore Shyam's share = (441/841) * 5887 = 3087

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17 24118
Q:

The compound interest on a sum of money for 2 years is rs.832 and the simple interest on the same sum for the same period is rs.800 .the difference between the compound interest and simple interest for 3 years

A) Rs.48 B) Rs.66.56
C) Rs.98.56 D) None of these
 
Answer & Explanation Answer: C) Rs.98.56

Explanation:

difference in C.I and S.I in 2years =Rs.32

S.I for 1year =Rs.400

S.I for Rs.400 for one year =Rs.32

rate=[100*32)/(400*1)%=8%

difference between in C.I and S.I for 3rd year

=S.I on Rs.832= Rs.(832*8*1)/100=Rs.66.56

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43 23887
Q:

If the compound interest on a certain sum at 1623% to 3 years is Rs.1270, find the simple interest on the same sum at the same rate and f or the same period.

A) 1080 B) 1090
C) 1180 D) 1109
 
Answer & Explanation Answer: A) 1080

Explanation:

Let the sum be Rs. x. Then,

 

 C.I=x*50300*1003-x=343x216-x=127x216 

 

127x216=1270 

 

x=2160 

 

Thus, the sum is Rs. 2160

 

 S.I=Rs.2160*503*3*1100=Rs 1080

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Q:

In what time will Rs. 1000 become Rs. 1331 at 10% per annum compounded annually?

A) 1years B) 2years
C) 3years D) 4years
 
Answer & Explanation Answer: C) 3years

Explanation:

Principal = Rs. 1000; Amount = Rs. 1331; Rate = 10% p.a. Let the time be n years. Then,
[ 1000 (1+ (10/100))^n ] = 1331 or (11/10)^n = (1331/1000) = (11/10)^3
n = 3 years

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