How long will it take a sum of money invested at 5% p.a. S.I. to increase its value by 40%?

A. 6 years
B. 7 years
C. 8 years
D. 9 years
Ans: C

Explanation: 

Let the sum be x. Then, S.I. = 40% of x = 2x/5; Rate = 5%.
Time = [100 * 2x/5 * 1/x*5]
        = 8 years.