A sum of money doubles itself in 8 years. What is the rate of interest?

Given :

A sum of money doubles itself in 8 years.

To do :

We have to find the rate of interest.

Solution :

Let the Principal be $P$ and rate percent be $R$.

This implies,

Amount $A=2P$

We know that,

$Amount (A) = Principal (P) + Simple Interest (SI)$

$Simple Interest (SI) = Amount (A) - Principal (P)$

$SI=2P-P$

$SI=P$                                  

$SI = \frac{PRT}{100}$

Therefore,

$P = \frac{(P \times R \times 8)}{100}$

$100 = R \times 8$

$R = \frac{100}{8}$

$R = 12.5$

The rate percent is 12.5%.