Solution: The GCF of 99 and 77 is 11
Methods
How to find the GCF of 99 and 77 using Prime Factorization
One way to find the GCF of 99 and 77 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 99?
What are the Factors of 77?
Here is the prime factorization of 99:
3
2
×
1
1
1
3^2 × 11^1
3 2 × 1 1 1
And this is the prime factorization of 77:
7
1
×
1
1
1
7^1 × 11^1
7 1 × 1 1 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 99 and 77 by multiplying all the matching prime factors to get a GCF of 99 and 77 as 121:
Thus, the GCF of 99 and 77 is: 121
How to Find the GCF of 99 and 77 by Listing All Common Factors
The first step to this method of finding the Greatest Common Factor of 99 and 77 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, 99 and 77:
Factors of 99: 1, 3, 9, 11, 33, 99
Factors of 77: 1, 7, 11, 77
When you compare the two lists of factors, you can see that the common factor(s) are 1, 11. Since 11 is the largest of these common factors, the GCF of 99 and 77 would be 11.
Find the GCF of Other Number Pairs
Want more practice? Try some of these other GCF problems:
What is the GCF of 135 and 76?
What is the GCF of 131 and 17?
What is the GCF of 64 and 66?
What is the GCF of 84 and 83?
What is the GCF of 24 and 109?