Chapter 6 - Factoring, Solving Equations, and Problem Solving - 6.1 - Factoring by Using the Distributive Property - Problem Set 6.1 - Page 242: 10

$7ab^3$

When we are looking for the greatest common factor, we are trying to find the greatest expression that can be multiplied by a whole number to get all three expressions. The greatest value that goes into $70a^3b^3$, $42a^2b^4$, and $49ab^5$ is $7ab^3$, so this is the greatest common factor.