Question

If the interest earned on a certain principal deposited is one-tenth of the principal (say P), determine the amount and rate of interest.

Answer 1

Amount = Principal + Interest
Given, interest is one-tenth of the principal (P).
Amount = Principal + Interest = $P+\frac{P}{10}=\frac{11P}{10}$
Again,
$\frac{\mathrm{Interest}}{\mathrm{Principal}}=\frac{\mathrm{Rate}}{100}\Rightarrow \frac{\frac{P}{10}}{P}=\frac{\mathrm{Rate}}{100}\Rightarrow \frac{1}{10}=\frac{\mathrm{Rate}}{100}\Rightarrow \mathrm{Rate}=10\%$