In how much time will an amount be doubled at the rate of $12.5\%$?

Let the Principal amount be $P$.
Since the amount doubles, the final Amount ($A$) will be $2P$.

Therefore, the Simple Interest ($\text{SI}$) earned is:

$$\text{SI}=A-P=2P-P=P$$

The formula for Simple Interest is:

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

Given the rate of interest ($R$) = $12.5\%$.
Substitute $\text{SI}=P$ and $R=12.5$ into the formula:

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

Dividing both sides by $P$:

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

$$T=\frac{100}{12.5}=8\text{ years}$$

Therefore, the amount will be doubled in $8\text{ years}$.