How do you find the greatest common factor of 55, 75?
By using the factors of the given numbers, we can find out the GCF.
Write down each of the numbers into its prime factors.
Now, circle the common factors of each of the numbers.
You get 5 common from both the numbers. Notice that after circling, you wont find anymore common factors so the GCF is simply 5. ( Each factor can be circled and used only once so 5 cannot be repeated even though 75 has two 5s.)