Name _____________________________________________________________________________________________________
Common Factors and GCF
R 7-3
You can use what you know about divisibility and fact families to help
you find the greatest common factor.
Find the greatest common factor of 9 and 12.
List all of the factors of each number. Remember to use divisibility rules.
Factors of 9: 1, 3, 9
Factors of 12: 1, 2, 3, 4, 6, 12
Then list the common factors, those numbers that are in both lists.
Common factors: 1, 3
The largest number in this list is 3. The greatest common factor (GCF)
of 9 and 12 is 3. The greatest common factor is sometimes called the greatest
common divisor (GCD).
The common factors of 9 and 12 are 1 and 3.
The greatest common factor (GCF) of 9 and 12 is 3.
The greatest number that can be in each group is 3.
List the factors of each number. Then find the GCF for each set of numbers.
1. 15
10
factors:
factors:
2. 24
GCF:
18
factors:
factors:
GCF:
3. 45
27
factors:
factors:
GCF:
© Scott Foresman, Gr. 5
(215)
Use with Chapter 7, Lesson 3.