#### Answer

$2x^{5}y^2$

#### Work Step by Step

Extracting the factors that are perfect powers of the index, the given expression simplifies to
\begin{array}{l}\require{cancel}
\sqrt[4]{16x^{20}y^8}
\\\\=
\sqrt[4]{(2x^{5}y^2)^4}
\\\\=
2x^{5}y^2
.\end{array}
Note that all variables are assumed to represent positive numbers.