At what time will a sum double itself, if the rate of interest is 5%?

The correct option is D 20 years
Given:
Rate = 5%

If, Principle = ₹ 100 then, Amount = ₹ 200.

$\therefore S.I=A-P=₹100$

$\because S.I=\frac{P\times R\times T}{100}$

$\Rightarrow T=\frac{S.I\times 100}{P\times R}$

$\Rightarrow T=\frac{100\times 100}{100\times 5}$

$\Rightarrow T=20\text{years}$

So, the time required is 20 years.