Answer
$5 \sqrt{5}$
Work Step by Step
In order to simplify a radical, we consider the factors of the number inside of the radical. If any of these factors are perfect squares, meaning that their square root is a whole number, then we can simplify the radical. We know that 25 and 5 are factors of 125. We know that 25 is a perfect square, so we simplify:
$ \sqrt{25} \sqrt{5}=5 \sqrt{5}$
