Question

The value of $\sqrt{20}\times \sqrt{5}$ is

(a) 10

(b) $2\sqrt{5}$

(c) $20\sqrt{5}$

(d) $4\sqrt{5}$

Answer 1

$$\begin{gathered} \sqrt{20}\times \sqrt{5} \\ =\sqrt{2\times 2\times 5}\times \sqrt{5} \\ =2\sqrt{5}\times \sqrt{5} \end{gathered}$$
$$\begin{gathered} =2\times 5 \\ =10 \end{gathered}$$
Hence, the correct answer is option (a).