Answer
$\dfrac{2}{\sqrt{10}}$
Work Step by Step
Rationalizing the numerator of $
\sqrt{\dfrac{2}{5}}
$ results to
\begin{array}{l}
\sqrt{\dfrac{2}{5}}
\cdot
\sqrt{\dfrac{2}{2}}
\\\\=
\sqrt{\dfrac{4}{10}}
\\\\=
\dfrac{2}{\sqrt{10}}
.\end{array}