Chapter 7 - Section 7.5 - Rationalizing Denominators and Numerators of Radical Expressions - Exercise Set - Page 445: 10

$\dfrac{5\sqrt{3a}}{9a}$

The rationalized form of $ \dfrac{5}{\sqrt{27a}} $ is \begin{array}{l} \dfrac{5}{\sqrt{27a}} \cdot\dfrac{\sqrt{3a}}{\sqrt{3a}} \\\\= \dfrac{5\sqrt{3a}}{\sqrt{81a^2}} \\\\= \dfrac{5\sqrt{3a}}{9a} .\end{array}