RRB NTPC - Compound Interest : Aptitude Test (65 Questions with Explanation)

1.

A sum of money is borrowed and paid back in two annual instalments of Rs.882 each allowing 5% compound interest .The sum borrowed was:

   A.) Rs.1640
   B.) Rs.1620
   C.) Rs.1680
   D.) Rs.1700

Answer: Option 'B'

Given
The sum borrowed
Present Worth of Rs.882 due 1 year + Present Worth of Rs.882 due 2 year
=> ( 882 ) / 1 + ( 5 / 100)1 + ( 882) / 1 + ( 5 / 100)1
=> (882 / 105 × 100 )1 + (882 / 105 × 100 )1
=> ( 882 /( 21 / 20 ) + ( 882 / (21 / 20)1
=> ( 882 × 20) / (21) + ( 882 × 20 × 20 / 21 × 21 )
=> 42 × 20 + 42 × 20 × 20 / 21
=> 840 + 2 × 20 × 20
=> 840 + 800
=> 1640
The sum borrowed = Rs.1640

2.

Find the simple interest on Rs. 1920 at 45 % per annum for 3 months

   A.) Rs. 196
   B.) Rs. 216
   C.) Rs. 206
   D.) Rs. 306

Answer: Option 'B'

Given
Principal : 1920
Rate of interest : 45
Number of months : 3
Simple interest for 1 year = pnr / 100
= ( 1920 x 1 x 45 ) / 100
= 864
Simple interest for 3 months = ( 3 / 12 ) x SI for 1 year
= ( 3 / 12 ) x 864
216

3.

Hari lended a sum of Rs.8000 for 20% per annum at compound interest then the sum of the amount will be Rs.13824 is obtained. After how many years he will get that amount? 

   A.) 2 years
   B.) 1 year
   C.) 4 years
   D.) 3 years

Answer: Option 'D'

Let Principal = P, Rate = R% per annum, Time = n years
When interest is compounded annually, total amount can be calculated by using the formula
Compound Amount = P ( 1 + R / 100)n
Given that, P = Rs.8000, R = 20% per annum
Compound Amount = Rs. 13824
We have to find the time period during which the amount will be Rs.13824
=> Rs.13824 = 8000 x (1 + 20/100)n
=> (13824 /8000) = (120 / 100)n
=> (24 / 20)3 = (12 / 10)n
=> (12 /10)3 = (12 /10 )n
Therefore, n = 3.
Hence the required time period is 3 years.

4.

Certain loan amount was repaid in two annual installments of Rs.1331/- each. If the rate of interest be 10% per annum Compounded annually the sum borrowed was?

   A.) Rs.121/-
   B.) Rs.2130/-
   C.) Rs.2310/-
   D.) Rs.1331/-

Answer: Option 'C'

Principal = (P.W of Rs. 1331/- due 1 year hence) + (P.W of Rs. 1331/- due 2 years hence) 
= [1331/(1 + 10/100) + 1331/(1 + 10/100)2
= [1331/(110/100) + 1331/(110/100 × 110/100)]
= 13310/11 + 133100/121 = 1210 + 1100 = Rs.2310/-

5.

Rs. 10000 is borrowed at compound interest at the rate of 4 % per annum. What will be the amount to be paid after 2 years ?

   A.) 10816
   B.) 10808
   C.) 10800
   D.) 10826

Answer: Option 'A'

Principal : P = 10000 Rs.
Rate of Interest : r = 4 %
Number of years : n = 2
Amount = P x (1 + r/100)n
Amount = 10000 x (1+4/100)2
=10000 x (1+1/25)2 =10000 x (26/25) x (26/25) =10816

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