Question

$\sqrt{10}\times \sqrt{15}=?$
(a) $\sqrt{25}$
(b) $5\sqrt{6}$
(c) $6\sqrt{5}$
(d) none of these

Answer 1

(b) $5\sqrt{6}$

$$\begin{gathered} \because \sqrt{10}\times \sqrt{15} \\ \therefore \sqrt{5\times 2}\times \sqrt{5\times 3} \\ =\sqrt{5}\times \sqrt{2}\times \sqrt{5}\times \sqrt{3} \\ =5\sqrt{6} \end{gathered}$$