Question

Solve: $2\sqrt{5}\times \sqrt{15}$.

Answer 1

$2\sqrt{5}\times \sqrt{15}=2\sqrt{5}\times \sqrt{5\times 3}$

$=2\sqrt{5^2\times 3}$

$=2\times 5\times \sqrt{3}=10\sqrt{3}$, which is the required solution.