Aptitude - Simple Interest
1.
At what rate of simple interest a certain sum will be doubled in 10 years ?
Answer
Let the sum be Rs. x. Then, S.I. = Rs. x
Rate =
100 x S.I.Sum x Time 
= 100 x xx x 10 % p.a. = 10% p.a.
Answer :
Option AExplanation :
Let the sum be Rs. x. Then, S.I. = Rs. x
Rate =
100 x S.I.Sum x Time = 100 x xx x 10 % p.a. = 10% p.a. 2.
A sum of money amounts to Rs. 5200 in 5 years and to Rs. 5680 in 7 years at simple interest. The rate of interest per annum is :
Answer
S.I. for 2 years = Rs. (5680 − 5200) = Rs. 480
S.I. for 1 year = Rs. 240
S.I. for 5 years = Rs. (240 x 5) = Rs. 1200
∴ Principal = Rs. (5200 − 1200) = Rs. 4000
∴ Rate = 1200 x 1004000 x 5 % p.a. = 6% p.a.
Answer :
Option DExplanation :
S.I. for 2 years = Rs. (5680 − 5200) = Rs. 480
S.I. for 1 year = Rs. 240
S.I. for 5 years = Rs. (240 x 5) = Rs. 1200
∴ Principal = Rs. (5200 − 1200) = Rs. 4000
∴ Rate =
1200 x 1004000 x 5 % p.a. = 6% p.a. 3.
The sum of money that will give Rs. 1 as simple interest per day at the rate of 5% per annum, is :
Answer
Annual interest = Rs. 365, Rate = 5% p.a.
Sum = 100 x S.I.Rate x Time = 100 x 3655 x 1 = Rs. 7300
Answer :
Option CExplanation :
Annual interest = Rs. 365, Rate = 5% p.a.
Sum =
100 x S.I.Rate x Time = 100 x 3655 x 1 = Rs. 7300 4.
A farmer borrowed Rs. 3600 at 15% per annum. At the end of 4 years he cleared his account by paying Rs. 4000 and a goat. The cost of the goat is :
Answer
S.I. for 4 years = Rs. 3600 x 15 x 4100 = Rs. 2160
Amount after 4 years = Rs. (3600 + 2160) = Rs. 5760
Cost of goat = Rs. (5760 − 4000) = Rs. 1760
Answer :
Option DExplanation :
S.I. for 4 years = Rs.
3600 x 15 x 4100 = Rs. 2160Amount after 4 years = Rs. (3600 + 2160) = Rs. 5760
Cost of goat = Rs. (5760 − 4000) = Rs. 1760
5.
A commission agent allows a rebate of 10% to an investor while the company pays an interest of 9% on the investment. What rate of interest does the investor actually earn on his investment ?
Answer
Instead of Rs. 100, the investor invests = Rs. (100 − 10) = Rs. 90
Interest on Rs. 90 = Rs. 9
Interest on Rs. 100 = 9 x 10090 = Rs. 10 = 10%
Answer :
Option CExplanation :
Instead of Rs. 100, the investor invests = Rs. (100 − 10) = Rs. 90
Interest on Rs. 90 = Rs. 9
Interest on Rs. 100 = 9 x 10090 = Rs. 10 = 10%
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