Chapter 10 - Exponents and Radicals - 10.4 Dividing Radical Expressions - 10.4 Exercise Set - Page 654: 71

$\dfrac{2a^2}{\sqrt[3]{20ab}}$

Rationalizing the numerator, the given expression, $ \sqrt[3]{\dfrac{2a^5}{5b}} ,$ is equivalent to \begin{array}{l} \sqrt[3]{\dfrac{2a^5}{5b}\cdot\dfrac{4a}{4a}} \\\\= \sqrt[3]{\dfrac{8a^6}{20ab}} \\\\= \dfrac{2a^2}{\sqrt[3]{20ab}} .\end{array}