# A sum becomes its double in 10 years. Find the annual rate of simple interest.

A. 8% B. 5% C. 10% D. 20% Answer: Option C
Let Sum be Rs. x and Let S.I. = Rs. x Time = 10 years. $\begin{array}{l} \therefore \text { Rate }=\frac{\text { S.I. } \times 100}{\text { Principal } \times \text { Time }} \\ =\frac{x \times 100}{x \times 10} \\ =10 \% \text { per annum. } \end{array}$