You can use prime factorization to find the GCF of a set of numbers. This often works better for large numbers, where generating lists of all factors can be time-consuming.
Here’s how to find the GCF of a set of numbers using prime factorization:
* List the prime factors of each number.
* Circle every common prime factor — that is, every prime factor that’s a factor of every number in the set.
* Multiply all the circled numbers.
The result is the GCF.
For example, suppose you want to find the GCF of 28, 42, and 70. Step 1 says to list the prime factors of each number. Step 2 says to circle every prime factor that’s common to all three numbers (as shown in the following figure).
As you can see, the numbers 2 and 7 are common factors of all three numbers. Multiply these circled numbers together:
2 · 7 = 14
Thus, the GCF of 28, 42, and 70 is 14.