In how much time will an amount be tripled, at the rate of $25\%$ per annum simple interest?

Let the principal amount be $P$.
Since the amount triples itself, the final Amount ($A$) will be $3P$.

The Simple Interest ($\text{SI}$) earned is:

$$\text{SI}=A-P=3P-P=2P$$

Given:

$$\text{Rate of Interest (R)}=25\%\text{ per annum}$$

We know the formula for simple interest:

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

Substitute the values into the formula:

$$2P=\frac{P\times 25\times T}{100}$$

$$2=\frac{25T}{100}$$

$$2=\frac{T}{4}$$

$$T=2\times 4=8\text{ years}$$