![\"\"](\"http://www.mathskey.com/userfiles/image/steps_images/step1.JPG\")
Greatest common factor (GCF) is a factor that is greatest among the
\common factors of the numbers.
\List the factors of each number.
\Factors of 21: 3, 7, 21
\Factors of 42: 2, 3, 6, 7, 14, 21, 42
\Identify the greatest common factor.
\The greatest common factor of 21 and 42 is 21.![\"\"](\"http://www.mathskey.com/userfiles/image/steps_images/solution.JPG\")
The greatest common factor of 21 and 42 is 21.