1. 8 Greatest Common Factor
Objective: Finding Greatest Common Factor (GCF)
Vocabulary
The greatest common factor is the biggest factor that is common to two or more numbers
Method 1: Listing the factors
Find the GCF of 40 and 24
1, 2, 3, 4, 6, 8, 12, 24
24: 40:
What’s the biggest common factor?
1, 2, 4, 5, 8, 10, 20, 40 8

2. Method 2: Using prime factorization (factor trees)
Find the GCF of 36 and 48 48 36 6 8 6 6 2 4 3 2 2 3 2 3 2 2 2
36:
48:
2•2•3•3
The common factors are 2,2,and 3
2•2•2•2•3
The GCF is 2•2•

3. Method 3 Using prime factorization (upside down division)
Find the GCF of 45 and 60 60 5 45 2 3 9 2 30 3 15 3 5
3•3•5
2•2•3•5
The GCF is 3•5 = 15