Answer
$\dfrac{\sqrt{10xy}}{5y}$
Work Step by Step
Rationalizing the denominator of $
\sqrt{\dfrac{2x}{5y}}
$ results to
\begin{array}{l}
\sqrt{\dfrac{2x}{5y}}
\cdot
\sqrt{\dfrac{5y}{5y}}
\\\\=
\sqrt{\dfrac{10xy}{25y^2}}
\\\\=
\dfrac{\sqrt{10xy}}{5y}
.\end{array}