Solution: The GCF of 56 and 18 is 2
Methods
How to find the GCF of 56 and 18 using Prime Factorization
One way to find the GCF of 56 and 18 is to compare the prime factorization of each number. To find the prime factorization, you can follow the instructions for each number here:
What are the Factors of 56?
What are the Factors of 18?
Here is the prime factorization of 56:
2
3
×
7
1
2^3 × 7^1
2 3 × 7 1
And this is the prime factorization of 18:
2
1
×
3
2
2^1 × 3^2
2 1 × 3 2
When you compare the prime factorization of these two numbers, you can see that there are matching prime factors. You can now find the Greatest Common Factor of 56 and 18 by multiplying all the matching prime factors to get a GCF of 56 and 18 as 4:
Thus, the GCF of 56 and 18 is: 4
How to Find the GCF of 56 and 18 by Listing All Common Factors
The first step to this method of finding the Greatest Common Factor of 56 and 18 is to find and list all the factors of each number. Again, you can see how this is done by looking at the “Factors of” articles that are linked to above.
Let’s take a look at the factors for each of these numbers, 56 and 18:
Factors of 56: 1, 2, 4, 7, 8, 14, 28, 56
Factors of 18: 1, 2, 3, 6, 9, 18
When you compare the two lists of factors, you can see that the common factor(s) are 1, 2. Since 2 is the largest of these common factors, the GCF of 56 and 18 would be 2.
Find the GCF of Other Number Pairs
Want more practice? Try some of these other GCF problems:
What is the GCF of 122 and 22?
What is the GCF of 128 and 138?
What is the GCF of 36 and 81?
What is the GCF of 143 and 94?
What is the GCF of 119 and 14?