Chapter 9 - Roots and Radicals - 9.1 - Roots and Radicals - Problem Set 9.1 - Page 401: 78

$\approx17.9$

Using the properties of radicals, a rational approximation (to the nearest tenth) of the given expression, $ 9\sqrt{5}-2\sqrt{5}+\sqrt{5} ,$ is \begin{array}{l}\require{cancel} (9-2+1)\sqrt{5} \\\\= 8\sqrt{5} \\\\ \approx17.9 .\end{array}