Answer
$\displaystyle \frac{5\sqrt{5y}}{xy}$
Work Step by Step
Simpify the denominator using
$\sqrt[n]{a}\times\sqrt[n]{b}=\sqrt[n]{ab},\qquad$ and
$\sqrt[n]{a^{n}}=(\sqrt[n]{a})^{n}=a$ (for positive a).
$\sqrt{5x^{2}y}=\sqrt{x^{2}\times 5y}=\sqrt{x^{2}}\times\sqrt{5y} = x\sqrt{5y}$
$... =\displaystyle \frac{25}{x\sqrt{5y}}$ $\displaystyle \color{red}{ \cdot\frac{\sqrt{5y}}{\sqrt{5y}} }\qquad$ (rationalize)
$=\displaystyle \frac{25\sqrt{5y}}{x(\sqrt{5y})^{2}}$
$=\displaystyle \frac{25\sqrt{5y}}{x(5y)}$ $\qquad$ ... reduce 5, the common factor
= $\displaystyle \frac{5\sqrt{5y}}{xy}$
