Download Lesson 1.5 Greatest Common Factor

Common Factors are factors that are shared between two lists of factors.
Greatest Common Factor (GCF) is the greatest (or highest) number in a list
of common factors
Venn Diagram


Create a Venn Diagram
and put each number in
its own circle
List the factors of each
number and put the
common factors in the
overlap of the circles
Find the GCF of 28 & 42
28
1,2
4, 28
7,14
42
3, 6

Write the prime
factorization of each
number

Circle the common prime
factors

Find the product of the
common prime factors
28: 1, 2, 4, 7, 14, 28
42: 1, 2, 3, 6, 7, 14, 21, 42
List the Factors

List all the factors of each
number

Find the common factors

Identify the GCF
21, 42
Common Factors: 1,2,7,14
GCF: 14
Prime Factorization
 Make a factor tree for each
number
Find the GCF of 28 & 42
Find the GCF of 28 & 42
28
42
4•7
6•7
2•2
2•3
2• 2 • 7
2• 3 • 7
GCF: 2• 7 = 14
GCF: 14
Find the GCF of 28 & 42
2 28
Repeated Division

Divide both numbers by a
common factor until the
only common factor is 1

Find the product of only
the common factors
42
7 14
21
2
3
GCF: 2• 7 = 14