Simple Interest Problems

Simple Interest Problems 

Dear Reader,
Below are four problems on simple interest with calculations on principal, rate and time duration.

Question 1

A man lent out Rs.9600 at 9/2 % per annum for a year and 9 months. At the end of the duration, the amount he earned as S.I was:

a) Rs. 567 b) Rs.756 c) Rs.874 d) Rs.784

Answer : b) Rs.756

Solution :
Given that, principal = P = Rs.9600, R = 9/2 % and T = 1 year and 9 months = 1 + 9/12 year = 7/4 years.
Now, we have to find the S.I for 7/4 years.
S.I = PRT/100 = Rs. 9600 x 9/2 x 7/4 x 1/100 = 12 x 9 x 7 = 756
Hence, the required S.I amount is Rs.756

Question 2

A man borrowed Rs.33600 at 25/4 % per annum on September 2012 and he paid back in May 2013. Find the amount he paid as S.I.

a) Rs.2075 b) Rs.2575 c) Rs.1575 d) Rs.1975

Answer : c) Rs.1575.

Solution :
Given that, principal = P = Rs. 33600 and R = 25/4 %.
Time duration = From September 2012 to May 2013 = 9 months = 9/12 year = 3/4 year.
S.I = PRT/100 = Rs. 33600 x 25/4 x 3/4 x 1/100 = 21 x 25 x 3 = Rs.1575.
Hence, the answer is Rs.1575.

Question 3

How much time will it take for a sum of Rs. 9000 to yield Rs. 1620 as S.I at 4 1/2 % per annum?

a) 1 year b) 2 years c) 3 years d) 4 years

Answer : d) 4years.

Solution :

Given that, Principal = P = Rs. 9000, S.I = Rs. 1620 and rate R = 4 1/2 % = 9/2 %
We have to find T.
T = S.I x 100/PR = 1620 x 100/9000 x (9/2)
= 162x2 / 9x9 = 4
Therefore, required time is 4 years.

Question 4

At what rate of simple interest, a sum of Rs.8540 amounts to Rs.9710 in 3 years?

a) 3 1/2 % b) 2 1/4 % c) 3 3/4 % d) 4 1/2 %

Answer : d) 4 1/2 %

Solution :

Given that, principal = P = Rs. 8540
Final amount = Rs. 9710
Then, interest = S.I = Rs.9710 – Rs.8540 = Rs. 1170.
Time = T = 3 years.
Required rate = R = S.I x 100 / PxT = 1170 x 100 / 8540 x 3 = 1950/427
= 4.566 = 4.5 (approximately) = 9/2 = 4 1/2 %
Hence, the answer is 4 1/2 %.