#### Answer

$\sqrt[]{3a}$

#### Work Step by Step

Using $a^{m/n}=\sqrt[n]{a^m}=(\sqrt[n]{a})^m$, the given expression, $
\left( \sqrt[10]{3a} \right)^5
,$ is equivalent to
\begin{array}{l}\require{cancel}
(3a)^{5/10}
\\\\=
(3a)^{1/2}
\\\\=
\sqrt[]{(3a)^1}
\\\\=
\sqrt[]{3a}
.\end{array}