Answer
$12$
Work Step by Step
Factor each number completely to obtain:
$60 = 2 \cdot 2 \cdot 3 \cdot 5
\\72 = 2 \cdot 2 \cdot 2 \cdot 3 \cdot 3$
Since two 2s and one 3 are common to both, the greatest common factor of the two given numbers is:
$2 \cdot 2 \cdot 3 = 12$
