Question:
The value of $\sqrt{20} \times \sqrt{5}$ is
(a) 10
(b) $2 \sqrt{5}$
(c) $20 \sqrt{5}$
(d) $4 \sqrt{5}$
Solution:
$\sqrt{20} \times \sqrt{5}$
$=\sqrt{2 \times 2 \times 5} \times \sqrt{5}$
$=2 \sqrt{5} \times \sqrt{5}$
$=2 \times 5$
$=10$
Hence, the correct answer is option (a).