1. 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.

2. Method 1: Listing the Factors
Find the GCF of 24 and 40
What’s the biggest common factor? 24 1 2 12 3 8 4 6 40 1 2 20 4 10 5 8
The GCF of 24 and 40 is 8.

3. Method 2: Using Prime Factorization; “Upside-Down division”
Find the GCF of 45 and 60
The common prime factors are 3•5; The GCF is 15 45 3 2 60 3 15 2 30 5 3 15 5
45: 3•3•5
60: 2•2•3•5

4. Method 3: Using Prime Factorization; Factor Trees
Find the GCF of 36 and 48
The common prime factors are 2•2•3; The GCF is 12 36 48
36: 2•2•3•3
48: 2•2•2•2•3