Solution: The GCF of 55 and 40 is 5
Methods
How to find the GCF of 55 and 40 using Prime Factorization
One way to find the GCF of 55 and 40 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 55?
What are the Factors of 40?
Here is the prime factorization of 55:
5
1
×
1
1
1
5^1 × 11^1
5 1 × 1 1 1
And this is the prime factorization of 40:
2
3
×
5
1
2^3 × 5^1
2 3 × 5 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 55 and 40 by multiplying all the matching prime factors to get a GCF of 55 and 40 as 25:
Thus, the GCF of 55 and 40 is: 25
How to Find the GCF of 55 and 40 by Listing All Common Factors
The first step to this method of finding the Greatest Common Factor of 55 and 40 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, 55 and 40:
Factors of 55: 1, 5, 11, 55
Factors of 40: 1, 2, 4, 5, 8, 10, 20, 40
When you compare the two lists of factors, you can see that the common factor(s) are 1, 5. Since 5 is the largest of these common factors, the GCF of 55 and 40 would be 5.
Find the GCF of Other Number Pairs
Want more practice? Try some of these other GCF problems:
What is the GCF of 148 and 39?
What is the GCF of 13 and 125?
What is the GCF of 83 and 74?
What is the GCF of 20 and 50?
What is the GCF of 127 and 30?