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Calculate the Greatest Common Factor or GCF of 21

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The instructions to find the GCF of 21 are the next:

1. Decompose all numbers into prime factors

213
77
1

2. Write all numbers as the product of its prime factors

Prime factors of 21=3 . 7

3. Choose the common prime factors with the lowest exponent

Common prime factors: 3 , 7

Common prime factors with the lowest exponent: 31, 71

4. Calculate the Greatest Common Factor or GCF

Remember, to find the GCF of several numbers you must multiply the common prime factors with the lowest exponent.

GCF = 31. 71 = 21


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