Chapter 6 - Section 6.1 - The Greatest Common Factor and Factoring by Grouping - Exercise Set - Page 427: 8

$5y$

The $GCF$ of $ 10,20 $ and $ -5 $ is $ 5 .$ The $GCF$ of $ y^5,y^2, $ and $ y $ is $ y .$ Hence, the $GCF$ of the given expressions, $ 10y^5,20y^2, \text{ and } -5y ,$ is \begin{array}{l}\require{cancel} 5y .\end{array}