In how many years will a sum of money double itself at 12.5% p.a., at simple interest?

8 years

The correct answer is Option (4) → 8 years

For a sum to double at simple interest, the interest earned must equal the principal.

Using the formula:

$\text{SI} = \frac{P \times R \times T}{100}$​

Set SI = P:

$\frac{P \times 12.5 \times T}{100} = P$

Cancel PPP:

$\frac{12.5 \times T}{100} = 1$

$T = \frac{100}{12.5} = 8T=12.5100​=8$

Correct answer: 8 years