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The GCF of 21 and 45 is 3.

One way to determine the greatest common factor is to find all the factors of the numbers and compare them.

The factors of 21 are 1, 3, 7, and 21.

The factors of 45 are 1, 3, 5, 9, 15, and 45.

The common factors are 1 and 3. Therefore, the greatest common factor is 3.

The greatest common factor can also be calculated by identifying the common prime factors and multiplying them together.

The prime factors of 21 are 3 and 7.

The prime factors of 45 are 3, 3, and 5.

The prime factors in common are a single 3, so the greatest common factor is 3.

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9y ago

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