Math
posted by Brandi on .
I want to make sure I'm doing the GCF correctly with 3 numbers. The problem is: Ari is making patriotic pins. He has 105 red ribbons, 147 white ribbons, and 189 blue ribbons. What is the greatest number of identical pins he can make if he uses all his ribbons? I think the answer is 21. Is that correct? Thanks..

21 is correct.
When in doubt, do one of the following:
1. Find GCF for two numbers at a time, the first time using two original numbers. The second time use the first GCF and the third number.
2. Divide each original number by the GCF found. If the numbers don't divide, there is a mistake. If there is a GCF between the three GCFs, then some factors were missing from the original GCF.