# If a sum of money double itself in 8 years, then the interest rate in percentage is ?

A. $8 \frac{1}{2} \%$ B. $10 \%$ C. $10 \frac{1}{2} \%$ D. $12 \frac{1}{2} \%$ Answer: Option D
Money is double itself means interest is equal to money. $\begin{array}{l} \mathrm{P}=\frac{\mathrm{P} \times 8 \times \mathrm{r}}{100} \\ \Rightarrow \mathrm{r}=\frac{100}{8} \\ \Rightarrow \mathrm{r}=12 \frac{1}{2} \% \end{array}$