# 5-15 Greatest Common Factor

### Lesson List

The Greatest Common Factor of two numbers will help you change a fraction into lowest terms.  Let's look at the Greatest Common Factor (GCF) of the fraction.

16
24

Begin by listing the factors of each number.

 Factors of 16: 1, 2, 4, 8, 16 Factors of 24: 1, 2, 3, 4, 6, 8, 12, 24 The common factors of 16 and 24 are 1, 2, 4, & 8. The GCF of 16 and 24 is 8.

List the factors for the fraction 8/12.
The factors of 8 are: 1, 2, 4, 8.
The factors of 12 are: 1, 2, 3, 4, 6, 12.
The GCF is

List the factors for the fraction 6/18.
The factors of 6 are: 1, 2, 3, 6.
The factors of 18 are: 1, 2, 3, 6, 9, 18.
The GCF is

List the factors for the fraction 14/21.
The factors of 14 are: 1, 2, 7, 14.
The factors of 21 are: 1, 3, 7, 21.
The GCF is

List the factors for the fraction 15/45.
The factors of 15 are: 1, 3, 5, 15.
The factors of 45 are: 1, 3, 5, 9, 15, 45.
The GCF is

List the factors for the fraction 9/21.
The factors of 9 are: 1, , 9.
The factors of 21 are: 1, , , 21.
The GCF is

List the factors for the fraction 20/30.
The factors of 20 are: 1, , , , , .
The factors of 30 are: 1, , , , , , , .
The GCF is

List the factors for the fraction 16/24.
The factors of 16 are: , , , , .
The factors of 24 are: , , , , , , , .
The GCF is

List the factors for the fraction 28/54.
The factors of 28 are: , , , , , .
The factors of 54 are: , , , , , , , .
The GCF is

List the factors for the fraction 15/48.
The factors of 15 are: , , , .
The factors of 48 are: , , , , , , , , , .
The GCF is

List the factors for the fraction 24/64.
The factors of 24 are: , , , , , , , .
The factors of 64 are: , , , , , , .
The GCF is