The simple interest on a sum of money is $$\frac{1}{4}$$ of the principal and the number of years is equal to rate percent per annum. The rate percent is =
a) 2.5%
b) 5%
c) 7.5%
d) 10%

Answer: b
Explanation:
$$\eqalign{ & {\text{Principal}}\,\,\,\,\,{\text{Interest}} \cr & \underbrace {\,\,\,\,\,\,\,4{\text{P}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{\text{P}}\,\,\,\,\,\,\,\,\,\,}_{} \cr & {\text{Time = Rate }}\% {\text{ (given)}} \cr & {\text{Now using formula , }} \cr & {\text{P = }}\frac{{4{\text{P}} \times {\text{R}} \times {\text{R}}}}{{100}} \cr & {{\text{R}}^2} = \frac{{100}}{4} \cr & {\text{R = }}\frac{{10}}{2} \cr & {\text{R = 5}}\% \cr} $$