- ✓$8\%$
- B$4\%$
- C$6\%$
- D$12\%$
Let the sum $(P)$ be $Rs. x$
Then, the simple interest $(I) =\text{Rs.}\frac{16}{25}\text{x}$
Also,
Rate $(R) = R\%$
Time $(T) = R$ years $(\because$ the rate percent per annum and the time are numerically equal$)$
$\text{I}=\frac{\text{P}\ \times\ \text{R}\ \times\ \text{T}}{100}$
$\Rightarrow\text{R}=\frac{100\ \times\ \text{I}}{\text{P}\ \times\ \text{T}}$
$\Rightarrow\text{R}=\frac{100\ \times\ \frac{16}{25}\text{x}}{\text{x}\ \times\ \text{R}}$
$\Rightarrow\text{R}\ \times \text{R}=\frac{{64\text{x}}}{\text{x}}$
$\Rightarrow\text{R}^2=8^2$
$\Rightarrow\text{R}=8\%$
Hence, the correct option is $(a).$