GCF and LCM Review

​The Greatest Common Factor, or GCF, is the greatest factor that divides two numbers.

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1.​ List the prime factors of each number.

2. Multiply the factors they have in common. If there are no

common prime factors, the GCF is 1.

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OR

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​1. List all of the possible factors for each number.

​2. Find the biggest number they have in common.

​Prime Factors of 18: 2 x 3 x 3

Prime Factors of 24: 2 x 2 x 2 x 3

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There is one 2 and one 3 in common.

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The GCF is 2 x 3 = 6

​Find the GCF of 14 and 49.

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Factors of 14: 2 x 7

Factors 49: 7 x 7

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7 is the only common factor, so the GCF is 7.

​A common multiple is a number that is a multiple of two or more numbers. The common multiples of 3 and 4 are 12, 24, ....

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The least common multiple (LCM) of two numbers is the smallest number (not zero) that is a multiple of both.

​Multiples of 3:

3, 6, 9, 12, 15, 18, 21, 24

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Multiples of 4:

4, 8, 12, 16, 20, 24

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The LCM of 3 and 4 is 12.

​GCF = biggest number that divides into

both chosen numbers

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​LCM = smallest number that both

chosen numbers multiply to