## Elementary Algebra

$-40$
We first multiply the separate square roots together to create one square root. Then, we simplify $\sqrt{16}$ because it is a perfect square: $-5\sqrt 8 \times 2\sqrt 2$ =$(-5\times2)\times(\sqrt 8\times\sqrt 2)$ =$(-10)\times(\sqrt {8\times2})$ =$(-10)\times(\sqrt {16})$ =$(-10)\times(\sqrt {4^{2}})$ =$(-10)\times(4)$ =$-40$