1. Greatest Common Factor
LESSON 4-4
Additional Examples
List the factors to find the GCF of 48 and 64.
List the factors of 48 and the factors of 64.
Factors of 48: 1 , 2 , 3, 4 , 6, 8 , 12, 16 , 24, 48
Factors of 64: 1 , 2 , 4 , 8 , 16 , 32, 64
Then circle the common factors.
The common factors are
1, 2, 4, 8, and 16.
The greatest common factor (GCF) is 16.

2. Greatest Common Factor
LESSON 4-4
Additional Examples
Use a division ladder to find the GCF of 84 and 90.
Divide by 2, a common factor of 84 and 90.
Divide by 3, a common factor of 42 and 45.
14 15
14 and 15 have no common factors.
Multiply the common factors: 2  3 = 6.
The GCF of 84 and 90 is 6.

3. Greatest Common Factor
LESSON 4-4
Additional Examples
Use factor trees to find the GCF of 28 and 42.
Make a factor tree for each number.
2 14
2 7 28
7 2
14 3 42
Write the prime factorization for each number.
28 =
42 = 
Identify common factors.
2  7 = 14 Multiply the common factors.
The GCF of 28 and 42 is 14.