Answer
$$9\ painters .$$
Work Step by Step
Since the number of people working on a project and the time it takes to complete a project vary inversely, then we can set up an inverse relationship as:
(no. of painters)(days)=(no. of painters)(days)
Thus, we have
$$ 3\times 24=x\times 8\Longrightarrow x=\frac{3\times 24}{8}=9\ painters .$$
