Answer
$4x^{1/4}$
Work Step by Step
$\displaystyle \frac{20x^{1/2}}{5x^{1/4}}=\frac{20}{5}\cdot\frac{x^{1/2}}{x^{1/4}}\qquad$... apply $\displaystyle \frac{a^{m}}{a^{n}}=a^{m-n}$
$=4\cdot x^{1/2-1/4}\qquad$...$\displaystyle \frac{1}{2}-\frac{1}{4}=\frac{2-1}{4}$ ...
$=4x^{1/4}$
