Question

Mark (✓) against the correct answer
At what rate per cent per annum simple interest will a sum double itself in 10 years?

(a) 8%
(b) 10%
(c) 12%
(d) $12\frac{1}{2}\%$

Answer 1

$$\begin{gathered} \text{(b) 10\%} \\ \begin{array}{l}\text{Let the sum be Rs}x.\\ \text{Amount=Rs 2}x\\ \text{Time=10 years}\\ \therefore \text{S}\text{.I}\text{.=A}-\text{P=2}x-x\\ \text{=Rs}x\\ \therefore \text{S}\text{.I.=}\frac{\text{P}\times \text{R}\times \text{T}}{100}\\ =>x=\frac{x\times \text{R}\times \text{10}}{100}\\ =>\text{R=}\frac{\sout{x}\times \sout{1}\sout{0}\sout{0}}{\sout{x}\times \sout{1}\sout{0}}\end{array} \\ =>\mathrm{R}=10 \end{gathered}$$