Question

A sum of money doubles itself in 5 years at a certain rate of interest. How many years will it take for a certain sum to become 3 times itself at the same rate of interest?​

Answer 1

$Let \: sum=x \: \: then \: S.I=x$

$Rate = \frac{100 \times S.I}{P \times T} \\ \\ = \frac{100 \times x}{x \times 5} \\ \\ = 20 \: \%$

$Now \: for \: case \: se cond \\ \\ sum=x, \: SI=2x$

$Time = \frac{2x \times 100}{x \times 20} \\ \\ Time = \frac{200x}{20x} \\ \\ Time = 10 \: years$