Question

A sum of money lent on simple interest, becomes $\frac{7}{5}$ of itself in 4 years. Find the rate of interest per annum.

Answer 1

Let the sum of money (Principal) $=₹x$
$\therefore$ Amount $\left(A\right)=\frac{7}{5}\times ₹x=₹\frac{7x}{5}$
Simple interest $\left(I\right)$ earned $=A-P$
$=₹\frac{7x}{5}-₹x=₹\frac{2x}{5}\text{Rate\%}=\frac{100\times I}{P\times T}\%=\frac{100\times \frac{2x}{5}}{x\times 4}\%=\frac{100\times 2x}{x\times 4\times 5}\%=10\%$