# How do you find the greatest common factor of 9, 6, and 42?

3

#### Explanation:

When I do GCF questions, I first like to have the prime factorization of the numbers in question:

$9 = 3 \times 3$
$6 = 3 \times 2$
$42 = 2 \times 3 \times 7$

The GCF asks us to find the largest number we can make using all the primes that are shared by all the numbers in question. In this case, the only prime that all three of our numbers have in common is a single 3. So that's the GCF.