Answer
$2$
Work Step by Step
To solve the item mentally, note that:
$\sqrt{0.1}\cdot\sqrt{40} = \sqrt{0.1(40)}=\sqrt{4}$ (because of the product rule for radicals)
Since $4=2^2$. then
$\sqrt{4} = \sqrt{2^2} = 2$
Thus.
$\sqrt{0.1}\cdot\sqrt{40}=2$
