A man can row upstream at $8\text{kmph}$ and downstream at $13\text{kmph}$. The speed of the stream is:

We are given:
* Upstream speed ($U$) = $8\text{kmph}$
* Downstream speed ($D$) = $13\text{kmph}$

The formula to calculate the speed of the stream is:

$$\text{Speed of the stream}=\frac{D-U}{2}$$

Substituting the given values into the formula:

$$\text{Speed of the stream}=\frac{13-8}{2}=\frac{5}{2}=2.5\text{kmph}$$