Write the factors both numbers have in common in the overlapping section of the Venn Diagram circles. Write the remaining factors for the number on the left in the left circle, and the remaining factors for the number on the right in the right circle. Look at the overlapping section and write the G.C.F. (Greatest Common Factor) on the line below each Venn Diagram.
Check out this Greatest Common Factor Stations activity, which is great for reviewing before a quiz/test and keeps students engaged:
Greatest Common Factor Stations