A sum of money becomes $\dfrac{7}{5}$ of itself in 4 years at a certain rate of simple interest. The rate per annum is :
9%
10%
11%
12%
Explanation:
Let the sum of money be Rs.x
$\text{Amount after 4 years = }\dfrac{7x}{5}$
T = 4 years
R = ?
$\text{Simple Interest, SI = }\left(\dfrac{7x}{5} - x\right) = \dfrac{2x}{5}$
$\text{R = }\dfrac{100 \times \text{SI}}{\text{PT}} = \dfrac{100 \times \dfrac{2x}{5} }{x \times 4}= \dfrac{40}{4} = 10\%$