A radical can be separated in two or more radicals of the same order if it is possible to factorize the radicand.
$$\begin{array}{rcl} \sqrt{20}&=&\sqrt{4\cdot 5} = \sqrt{4} \cdot \sqrt{5}= \sqrt{2^2}\sqrt{5}=2^{\frac{2}{2}} \sqrt{5}=2\sqrt{5} \\ \displaystyle \frac{\sqrt{20}}{\sqrt{5}}&=&\displaystyle \frac{2\sqrt{5}}{\sqrt{5}}=2 \end{array}$$