You can find the greatest common factor (GCF) of 21 and 35 by listing the common factors for each number and then identifying the greatest factor in each list. Here's the step-by-step process:

Step 1: List the Factors of 21
• The factors of 21 are the numbers that can evenly divide 21. In this case, they are 1, 3, 7, and 21.

Step 2: List the Factors of 35
• The factors of 35 are the numbers that can evenly divide 35. In this case, they are 1, 5, 7, and 35.

Step 3: Identify the Common Factors
• Compare the lists of factors for 21 and 35 to find the common factors. The common factors are the numbers that appear in both lists.
Common Factors: 1, 7

Step 4: Determine the Greatest Common Factor
• Finally, determine which common factor is the greatest. In this case, the greatest common factor (GCF) of 21 and 35 is 7.
So, the GCF of 21 and 35 is 7.

Note: You can also use prime factorization to find the GCF. It involves breaking down each number into its prime factors and then finding the common prime factors.

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