Interactive Greatest Common Factor Activity

The new interactive greatest common factor activity at helps students master the process of finding the greatest common factor. This interactive activity can be used as either an online or offline activity. In the online mode student can enter their answer directly in the activity and the computer will tell them when they have the correct answer. They can keep changing their answer until they get it correct. This will help students master the process of finding greatest common factors. The page starts out with 6 problems and more problems can be added.

To use the offline mode simply print the page and the computer takes care of making sure that it is nicely formatted. After you have printed the worksheet make sure to click the answer key to fill in all of the correct answers and then you can print your answer key. Both the worksheet and answer key have the same timestamp to help you keep track of which answer key goes with which worksheet.

The program makes sure that their are no duplicate questions.

Tips for finding greatest common factors. 
Find the factors of each number just as described in the factors activity the largest number in both lists is you answer.

Make a factor tree of both numbers and cross out the leaves not in both trees. Multiply the leaves in one tree together and that is your greatest common factor.

Example:
Find the GCF of 12 and 16.

Factor Tree of 12  2 × 6 2 × 2 × 3 Common leaves 2 × 2 × 3

Find the GCF of 16 4 × 4 2 × 2 × 2 × 2 Common leaves 2 × 2 × 2 × 2

Multiply the common leaves together: 2 × 2 = 4. Therefor the greatest common factor is 4.

Remember the tips for finding factors 2 through 10.
2: If the last digit of the number is even (0,2,4,6,8)then then number is divisible by 2.

3: If the sum of the digits is divisible by 3 then the number is divisible by 3. For example 21 would be 2 + 1 = 3 which is divisible by 3 so 21 is divisible by 3.

5: If the last digit of the number is 5 or 0 then the number is divisible by 5.

6: If the number is divisible by 2 and 3 the number is divisible by 6.

10: If the last digit of the number is 0 then the number is divisible by 10.