If a certain sum of money becomes doubles at simple interest in 12 years, what would be the rate of interest per annum?

Answer: Option A

Let,
Principal, P = Rs. 100;
Amount, A = Rs. 200;
Time = 12 years;
Interest = Rs. 100;
Rate of interest
$$\begin{array}{rl}& =\frac{\text{Total Interest}}{\text{Given Time}}\\ & =\frac{100}{12}\\ & =8\frac{1}{3}\%\end{array}$$