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5.4: The Greatest Common Factor

  • Page ID
    51010
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    Definition: Greatest Common Factor (GCF)

    The Greatest Common Factor (GCF) of two or more whole numbers is the largest number that is a factor of the two or more numbers.

    To find the GCF, we work backwards, following the three steps below.

    clipboard_ec0d69c72cbc6cd3498959cdb269bd39d.png
    Figure 5.4.1: Steps to find GCF

    Example \(\PageIndex{1}\)

    Find the GCF of 54 and 60

    Solution

    Step 1: List all the Factors, starting with 2

    54 → 2, 3, 6, 9, 18, 27, 54

    60 → 2, 3, 4, 5, 6, 10, 12, 15, 20, 30, 60

    Step 2: Circle the Common factors

    clipboard_e33ba049a7c99d1ff15aecbdf03a224b8.png
    Figure 5.4.2

    Step 3: Choose the Greatest circled pair

    Answer: GCF (54, 60) = 6

    Example \(\PageIndex{2}\)

    Write the Simplest Form of the Fraction using the GCF \(\dfrac{140}{165}=?\). \(\text {GCF}(140,165)=5\)

    Solution

    Divide top and bottom by 5.

    \[\dfrac{140}{165}=\dfrac{140 \div 5}{165 \div 5}=\dfrac{28}{33} \nonumber \]

    Partner Activity 1

    A forest ranger needs to remove three tree trucks by cutting the trunks into equal lengths. If the lengths of the tree trunks are six feet, eight feet and 12 feet, what is the length of the longest log that can be cut?

    clipboard_e9c96d8d987d5b005e0a274bd89805124.png
    Figure 5.4.3

    Partner Activity 2

    Rhys wants to organize his sports cards in packets for each type of sport. Each packet has the same number of cards. If he has 24 baseball cards, 60 hockey cards, and 48 football cards, find the greatest number of cards in each packet.

    clipboard_e9d4ac59c3b8c483d09d5e41dd4361b73.png
    Figure 5.4.4

    Practice Problems

    Find the Greatest Common Factor (GCF).

    1. 40 and 90
    2. 75 and 25
    3. 168 and 85
    4. 90, 120, and 150
    5. 135, 225, and 405

    This page titled 5.4: The Greatest Common Factor is shared under a not declared license and was authored, remixed, and/or curated by Amy Lagusker.

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