At simple interest, a sum doubles in 20 years. The rate of interest per annum is ____
A)5%
B)10%
C)12%
D)20%

Question

Quizplus · Accepted Answer

Simple Interest I = P x R x T . Sum doubles in 20 years. So interest I = P;
P=PxRxT R =1/T = (1/20 ) % = 5%
Key takeaway: Simple Interest is charged only on the original principal, not on the interest accrued. In compound interest, interest is given on interest also besides on the principle amount.

At Simple Interest, a Sum Doubles in 20 Years