Greatest Common Factor GCF

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Greatest Common Factor (GCF)
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The GCF of two or more numbers is the greatest
number that is a factor of each number
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Three ways to find GCF

• 1) Listing the Factors

• 2) Prime Factorization
• 3) Ladder method

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1) Listing the Factors
Step 1 List the factors of the numbers
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Example 24 and 36
36
24
1 36 2 18 3 12 4 9 6 6
1 24 2 12 3 8 4 6
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Step 2 List the common factors (the numbers
that are in both lists).
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Common Factors of 24 36 are
1, 2, 3, 4, 6, 12
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The largest is the greatest common factor
12
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2) Prime Factorization
Step 1 For each number draw a factor tree
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Example 24 and 36
36
24
4 6
6 6
2 3
2 2
2 3
2 3
12


2
2
3

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Using the Prime Factorization Method
The GCF is also 12
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3) Ladder method 2 144
48 2 72 24 2 36
12 6 18 6
1 3 1
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Multiply all common factors from outside of
divided by box.2 x 2 x 2 x 6 x 1GCF 48
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Find the Greatest Common Factor for the following
1) 8 and 24 2) 15 and 45
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Answers
1) GCF is 8
2) GCF is 15