A sum at simple interest becomes two times in 8 years at a certain rate of interest p.a. The time in which the same sum will be 4 times at the same rate of interest at simple interest is:

Answer: Option C

Formula used:
A = $$\text{P}\frac{\left(1+\text{RT}\right)}{100}$$
A → Amount
P → Principal
R → Rate
T → Time
Calculation:
A sum at simple interest becomes two times in 8 years
⇒ 2P = $$\frac{\text{P}\left(1+\text{R}\times \text{8}\right)}{100}$$
⇒ R = $$\frac{100}{8}$$
⇒ R = 12.5
∴ The rate of interest is 12.5%
The time in which the same sum will be 4 times
⇒ 4P = $$\frac{\text{P}\left(1+12.5\times \text{T}\right)}{100}$$
⇒ 300 = 12.5T
⇒ T = 24
∴ The sum will be 4 times in 24 years