Chapter 1 - Some Basic Concepts of Arithmetic and Algebra - 1.2 - Prime and Composite Numbers - Problem Set 1.2 - Page 13: 74

$16$

Factor each number completely to have: $32 = 2 \cdot 2 \cdot 2 \cdot 2 \cdot 2 \\80 = 2 \cdot 2 \cdot 2 \cdot 2 \cdot 5 \\96= 2 \cdot 2 \cdot 2 \cdot 2 \cdot 2 \cdot 3$ Since four 2s are common to both, the greatest common factor of the given numbers is: $2 \cdot 2\cdot 2\cdot 2 = 16$