Answer
$4 \sqrt{5}$
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 16 and 5 are factors of 80. We know that 16 is a perfect square, so we simplify:
$ \sqrt{16} \sqrt{5}=4 \sqrt{5}$
