What is the greatest common factor of 21 and 28?

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Multiple Choice

What is the greatest common factor of 21 and 28?

Explanation:
The greatest common factor is the largest number that can divide both numbers exactly. Factor each number: 21 = 3 × 7 and 28 = 2 × 2 × 7. They share the factor 7 (and 1, but 7 is the larger one). So the greatest common factor is 7. Numbers like 14, 21, or 28 don’t work because they don’t divide both numbers (14 doesn’t divide 21, 21 doesn’t divide 28, and 28 doesn’t divide 21).

The greatest common factor is the largest number that can divide both numbers exactly. Factor each number: 21 = 3 × 7 and 28 = 2 × 2 × 7. They share the factor 7 (and 1, but 7 is the larger one). So the greatest common factor is 7. Numbers like 14, 21, or 28 don’t work because they don’t divide both numbers (14 doesn’t divide 21, 21 doesn’t divide 28, and 28 doesn’t divide 21).

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