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

1.

What would be the compound interest accrued on an amount of 4500 Rs. at the end of 2 years at the rate of 10 % per annum?

   A.) 945
   B.) 5665
   C.) 5445
   D.) 435

Answer: Option 'A'

Given principal = 4500
No. of years = 2
Rate of interest = 10
Amount = P [ 1 + ( r / 100 ) ]n
= 4500 x [ 1 + ( 10 / 100 ) ]2
= 4500 x [ 1 + ( 1 / 10 ) ]2
= 4500 x [ 11 / 10 ]2
= 4500 x [ 121 / 100 ]
Amount = 5445
Compound interest = Amount - principal

= 5445 - 4500
= 945 Rs

2.

What would be the compound interest accrued on an amount of 4500 Rs. at the end of 2 years at the rate of 10 % per annum ?

   A.) 5435
   B.) 5445
   C.) 5665
   D.) 5345

Answer: Option 'B'

Given principal = 4500
No. of years = 2
Rate of interest = 10
Amount = P x (1+r/100)n,
We get Amount = 4500 x (1+10/100)2
Ans : 5445

3.

The difference between the compound interest and simple interest on a certain sum of money at 5% per annum for 2 years is 45. Then the original sum is? 

   A.) Rs.16000/-
   B.) Rs.15000/-
   C.) Rs.18000/-
   D.) Rs.20000/-

Answer: Option 'C'

For 2 years = (1002D)/R2
= (1002 × 45)/(5 × 5) = (10000 × 45)/25 = Rs.18000/-

4.

A person receives a sum of Rs. 210 as interest for investing some amount at 10% p.a compounding annually for 2 years. Find the amount invested at the beginning

   A.) 1050
   B.) 1000
   C.) 850
   D.) 950

Answer: Option 'B'

Given
Compound interest received by the person ( C.I ) = Rs. 210
Rate of interest ( r ) = 10 %
Number of years ( n ) = 2 years
To find, Amount invested at the beginning = principal ( p )
Compound interest ( C.I ) = Amount - Principal
Amount = p ( 1 + r / 100 )n

=> C.I = p [ ( 1 + r / 100 )n- 1 ]
=> 210 = p [ ( 1 + 10 / 100 )2- 1 ]
=> 210 = p [ ( 110 / 100 )2- 1 ]
=> 210 = p [ ( 11 / 10 )2- 1 ]
=> 210 = p [ ( 121 / 100 ) - 1 ]
=> 210 = p [ ( 121 - 100 ) / 100 ]
=> 210 = p [ 21 / 100 ]
=> 210 x ( 100 / 21 ) = p
=> 1000 = p
The amount invested at the beginning = p = Rs.1000

5.

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