2 and 9 are factors of 18.
When we have two or more given numbers, we can find the largest factor that both numbers have in common. This is called the GCF or the Greatest Common Factor.
There are several different methods that can be used to find the GCF. Let's take a look at some of the methods.
Method 1: List out the factors.
Example: Find the GCF of 64 and 96.
Step 1: List the factors of each number.
64: 1, 2, 4, 8, 16, 32, 64
96: 1, 2, 3, 4, 6, 8, 12, 16, 24, 32, 48, 96
Step 2: Look for factors that both lists have in common.
Step 3: Pick out the largest factor that both lists have in common and call this the GCF.
Therefore, the GCF of 64 and 96 is 32.
Method 2: Upside Down Division
Find the GCF of 280 and 144.
Step 1: Place the numbers inside an upside down division bar.
Step 2:Now, we need to divide both numbers by a common factor. Because both of the numbers are even, we could start with 2.The answer goes underneath the bar.
Step 3: We will continue to divide until we have two numbers that are relatively prime. Remember that relatively prime means two numbers that do not have any common factors other than 1.
35 and 18 are relatively prime.
Step 4: Now we take all of the factors on the side and multiply them together.
