Solution: The GCF of 20 and 86 is 2
Methods
How to find the GCF of 20 and 86 using Prime Factorization
One way to find the GCF of 20 and 86 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 20?
What are the Factors of 86?
Here is the prime factorization of 20:
2
2
×
5
1
2^2 × 5^1
2 2 × 5 1
And this is the prime factorization of 86:
2
1
×
4
3
1
2^1 × 43^1
2 1 × 4 3 1
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 20 and 86 by multiplying all the matching prime factors to get a GCF of 20 and 86 as 4:
Thus, the GCF of 20 and 86 is: 4
How to Find the GCF of 20 and 86 by Listing All Common Factors
The first step to this method of finding the Greatest Common Factor of 20 and 86 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, 20 and 86:
Factors of 20: 1, 2, 4, 5, 10, 20
Factors of 86: 1, 2, 43, 86
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 20 and 86 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 79 and 115?
What is the GCF of 138 and 99?
What is the GCF of 82 and 118?
What is the GCF of 122 and 127?
What is the GCF of 4 and 119?