![\"\"](\"http://www.mathskey.com/userfiles/image/steps_images/step1.JPG\")
Method 1:
\List the factors of each number.
\Factors of 20: 2, 4, 5, 10, 20
\\
Factors of 28: 2, 4, 7, 14, 28
\\
Factors of 36: 2, 3, 4, 6, 9, 12, 18, 36
\Identify the greatest common factor.
\The greatest common factor of 20, 28 and 36 is 4.
\![\"\"](\"http://www.mathskey.com/userfiles/image/steps_images/step2.JPG\")
Method 2:
\Write the prime factorization of each number.
\20 = 2 × 2 × 5 .
\28 = 2 × 2 × 7.
\36= 2 × 2 × 3 × 3.
\The GCF is the product of the common prime factors in each number.
\GCF = 2 × 2 = 4.
\The greatest common factor of 20, 28 and 36 is 4.
\![\"\"](\"http://www.mathskey.com/userfiles/image/steps_images/solution.JPG\")
The greatest common factor of 20, 28 and 36 is 4.