Identify all the factors of 9 and 15. Then choose the greatest common factor of 9 and 15. How do you know you chose correct greatest common factor?
The factors of 9 are 1, 3, and 9. The factors of 15 are 1, 3, 5, and 15.
To find the greatest common factor (GCF) of 9 and 15, we look for the highest number that appears in both lists of factors. In this case, the numbers that appear in both lists are 1 and 3. The GCF of 9 and 15 is 3.
We know that we chose the correct GCF because it is the highest factor that both numbers share, and it does not have any other factors in common with either number.