Question

At what rate of interest will a principal worth ₹3600 will amount to ₹4000 in one year ?

Answer 1

Amount = Principal + Interest
$\Rightarrow \mathrm{Interest}=\mathrm{Amount}-\mathrm{Principal}\Rightarrow \mathrm{Interest}=₹4000-₹3600=₹400$
We also know that,
$\frac{\mathrm{Interest}}{\mathrm{Principal}}=\frac{\mathrm{Rate}}{100}\Rightarrow \frac{400}{3600}=\frac{\mathrm{Rate}}{100}\Rightarrow \mathrm{Rate}=\frac{100}{9}\%$