What is the square root of 2 times the square root of 10?

$\sqrt{2} \sqrt{10} = \sqrt{20}$ =
$\sqrt{2 \times 2 \times 5}$ =
$\sqrt{2 \times 2} \sqrt{5}$ =
$\sqrt{4} \sqrt{5}$ =
$2 \sqrt{5}$