Greatest common factor (GCF)

  • Level: Grade 5 – Grade 6
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  • Answer key included

The greatest common factor is the largest number that divides both numbers exactly. It is used to simplify fractions. Finding the GCF of two numbers up to 100 is a sixth-grade standard (Common Core 6.NS.B.4).

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Grade 5 – Grade 6
Greatest common factor (GCF)

Find the greatest common factor.

Name Date Score / 16
  1. 1.
    GCF of 24 and 20 =
  2. 2.
    GCF of 6 and 27 =
  3. 3.
    GCF of 11 and 77 =
  4. 4.
    GCF of 54 and 6 =
  5. 5.
    GCF of 90 and 10 =
  6. 6.
    GCF of 49 and 14 =
  7. 7.
    GCF of 6 and 14 =
  8. 8.
    GCF of 20 and 16 =
  9. 9.
    GCF of 9 and 15 =
  10. 10.
    GCF of 12 and 24 =
  11. 11.
    GCF of 8 and 64 =
  12. 12.
    GCF of 10 and 70 =
  13. 13.
    GCF of 22 and 55 =
  14. 14.
    GCF of 10 and 90 =
  15. 15.
    GCF of 72 and 32 =
  16. 16.
    GCF of 25 and 45 =
MathSheetLab · mathlabs.pages.devWorksheet #792064
Grade 5 – Grade 6
Greatest common factor (GCF)Answer key
  1. 1.
    GCF of 24 and 20 = 4
  2. 2.
    GCF of 6 and 27 = 3
  3. 3.
    GCF of 11 and 77 = 11
  4. 4.
    GCF of 54 and 6 = 6
  5. 5.
    GCF of 90 and 10 = 10
  6. 6.
    GCF of 49 and 14 = 7
  7. 7.
    GCF of 6 and 14 = 2
  8. 8.
    GCF of 20 and 16 = 4
  9. 9.
    GCF of 9 and 15 = 3
  10. 10.
    GCF of 12 and 24 = 12
  11. 11.
    GCF of 8 and 64 = 8
  12. 12.
    GCF of 10 and 70 = 10
  13. 13.
    GCF of 22 and 55 = 11
  14. 14.
    GCF of 10 and 90 = 10
  15. 15.
    GCF of 72 and 32 = 8
  16. 16.
    GCF of 25 and 45 = 5
MathSheetLab · mathlabs.pages.devWorksheet #792064

About this worksheet

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Worked example

GCF of 20 and 24 =
  1. Factors of 20: 1, 2, 4, 5, 10, 20.
  2. Factors of 24: 1, 2, 3, 4, 6, 8, 12, 24.
  3. Common factors: 1, 2, 4. The greatest is 4.

Answer: 4

Teaching tips

  • List the factors of the smaller number first, from largest to smallest, and test each one on the larger number.

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