Name
Grade
School

Date
Questions20
Score

1

Find the GCF of 5 and 10

2

Find the GCF of 6 and 15

3

Find the GCF of 10 and 8

4

Find the GCF of 12 and 20

5

Find the GCF of 14 and 21

6

Find the GCF of 9 and 12

7

Find the GCF of 16 and 20

8

Find the GCF of 30 and 45

9

Find the GCF of 24 and 30

10

Find the GCF of 15 and 9

11

Find the GCF of 18 and 27

12

Find the GCF of 8 and 12

13

Find the GCF of 9 and 12

14

Find the GCF of 6 and 8

15

Find the GCF of 8 and 10

16

Find the GCF of 12 and 15

17

Find the GCF of 12 and 18

18

Find the GCF of 12 and 16

19

Find the GCF of 6 and 9

20

Find the GCF of 24 and 36

Answers Key

1

Find the GCF of 5 and 10

5 is the GCF of 5 and 10

Factors of 5

5 | 5 |

1 |

Factors of 10

2 | 10 |

5 | 5 |

1 |

Factors of 5 = 5

Factors of 10 = 2 x 5

Multiply all the common factors of 5 and 10.

5 = 5

GCF(5, 10) = 5

2

Find the GCF of 6 and 15

3 is the GCF of 6 and 15

Factors of 6

2 | 6 |

3 | 3 |

1 |

Factors of 15

3 | 15 |

5 | 5 |

1 |

Factors of 6 = 2 x 3

Factors of 15 = 3 x 5

Multiply all the common factors of 6 and 15.

3 = 3

GCF(6, 15) = 3

3

Find the GCF of 10 and 8

2 is the GCF of 10 and 8

Factors of 10

2 | 10 |

5 | 5 |

1 |

Factors of 8

2 | 8 |

2 | 4 |

2 | 2 |

1 |

Factors of 10 = 2 x 5

Factors of 8 = 2 x 2 x 2

Multiply all the common factors of 10 and 8.

2 = 2

GCF(10, 8) = 2

4

Find the GCF of 12 and 20

4 is the GCF of 12 and 20

Factors of 12

2 | 12 |

2 | 6 |

3 | 3 |

1 |

Factors of 20

2 | 20 |

2 | 10 |

5 | 5 |

1 |

Factors of 12 = 2 x 2 x 3

Factors of 20 = 2 x 2 x 5

Multiply all the common factors of 12 and 20.

2 x 2 = 4

GCF(12, 20) = 4

5

Find the GCF of 14 and 21

7 is the GCF of 14 and 21

Factors of 14

2 | 14 |

7 | 7 |

1 |

Factors of 21

3 | 21 |

7 | 7 |

1 |

Factors of 14 = 2 x 7

Factors of 21 = 3 x 7

Multiply all the common factors of 14 and 21.

7 = 7

GCF(14, 21) = 7

6

Find the GCF of 9 and 12

3 is the GCF of 9 and 12

Factors of 9

3 | 9 |

3 | 3 |

1 |

Factors of 12

2 | 12 |

2 | 6 |

3 | 3 |

1 |

Factors of 9 = 3 x 3

Factors of 12 = 2 x 2 x 3

Multiply all the common factors of 9 and 12.

3 = 3

GCF(9, 12) = 3

7

Find the GCF of 16 and 20

4 is the GCF of 16 and 20

Factors of 16

2 | 16 |

2 | 8 |

2 | 4 |

2 | 2 |

1 |

Factors of 20

2 | 20 |

2 | 10 |

5 | 5 |

1 |

Factors of 16 = 2 x 2 x 2 x 2

Factors of 20 = 2 x 2 x 5

Multiply all the common factors of 16 and 20.

2 x 2 = 4

GCF(16, 20) = 4

8

Find the GCF of 30 and 45

15 is the GCF of 30 and 45

Factors of 30

2 | 30 |

3 | 15 |

5 | 5 |

1 |

Factors of 45

3 | 45 |

3 | 15 |

5 | 5 |

1 |

Factors of 30 = 2 x 3 x 5

Factors of 45 = 3 x 3 x 5

Multiply all the common factors of 30 and 45.

3 x 5 = 15

GCF(30, 45) = 15

9

Find the GCF of 24 and 30

6 is the GCF of 24 and 30

Factors of 24

2 | 24 |

2 | 12 |

2 | 6 |

3 | 3 |

1 |

Factors of 30

2 | 30 |

3 | 15 |

5 | 5 |

1 |

Factors of 24 = 2 x 2 x 2 x 3

Factors of 30 = 2 x 3 x 5

Multiply all the common factors of 24 and 30.

2 x 3 = 6

GCF(24, 30) = 6

10

Find the GCF of 15 and 9

3 is the GCF of 15 and 9

Factors of 15

3 | 15 |

5 | 5 |

1 |

Factors of 9

3 | 9 |

3 | 3 |

1 |

Factors of 15 = 3 x 5

Factors of 9 = 3 x 3

Multiply all the common factors of 15 and 9.

3 = 3

GCF(15, 9) = 3

11

Find the GCF of 18 and 27

9 is the GCF of 18 and 27

Factors of 18

2 | 18 |

3 | 9 |

3 | 3 |

1 |

Factors of 27

3 | 27 |

3 | 9 |

3 | 3 |

1 |

Factors of 18 = 2 x 3 x 3

Factors of 27 = 3 x 3 x 3

Multiply all the common factors of 18 and 27.

3 x 3 = 9

GCF(18, 27) = 9

12

Find the GCF of 8 and 12

4 is the GCF of 8 and 12

Factors of 8

2 | 8 |

2 | 4 |

2 | 2 |

1 |

Factors of 12

2 | 12 |

2 | 6 |

3 | 3 |

1 |

Factors of 8 = 2 x 2 x 2

Factors of 12 = 2 x 2 x 3

Multiply all the common factors of 8 and 12.

2 x 2 = 4

GCF(8, 12) = 4

13

Find the GCF of 9 and 12

3 is the GCF of 9 and 12

Factors of 9

3 | 9 |

3 | 3 |

1 |

Factors of 12

2 | 12 |

2 | 6 |

3 | 3 |

1 |

Factors of 9 = 3 x 3

Factors of 12 = 2 x 2 x 3

Multiply all the common factors of 9 and 12.

3 = 3

GCF(9, 12) = 3

14

Find the GCF of 6 and 8

2 is the GCF of 6 and 8

Factors of 6

2 | 6 |

3 | 3 |

1 |

Factors of 8

2 | 8 |

2 | 4 |

2 | 2 |

1 |

Factors of 6 = 2 x 3

Factors of 8 = 2 x 2 x 2

Multiply all the common factors of 6 and 8.

2 = 2

GCF(6, 8) = 2

15

Find the GCF of 8 and 10

2 is the GCF of 8 and 10

Factors of 8

2 | 8 |

2 | 4 |

2 | 2 |

1 |

Factors of 10

2 | 10 |

5 | 5 |

1 |

Factors of 8 = 2 x 2 x 2

Factors of 10 = 2 x 5

Multiply all the common factors of 8 and 10.

2 = 2

GCF(8, 10) = 2

16

Find the GCF of 12 and 15

3 is the GCF of 12 and 15

Factors of 12

2 | 12 |

2 | 6 |

3 | 3 |

1 |

Factors of 15

3 | 15 |

5 | 5 |

1 |

Factors of 12 = 2 x 2 x 3

Factors of 15 = 3 x 5

Multiply all the common factors of 12 and 15.

3 = 3

GCF(12, 15) = 3

17

Find the GCF of 12 and 18

6 is the GCF of 12 and 18

Factors of 12

2 | 12 |

2 | 6 |

3 | 3 |

1 |

Factors of 18

2 | 18 |

3 | 9 |

3 | 3 |

1 |

Factors of 12 = 2 x 2 x 3

Factors of 18 = 2 x 3 x 3

Multiply all the common factors of 12 and 18.

2 x 3 = 6

GCF(12, 18) = 6

18

Find the GCF of 12 and 16

4 is the GCF of 12 and 16

Factors of 12

2 | 12 |

2 | 6 |

3 | 3 |

1 |

Factors of 16

2 | 16 |

2 | 8 |

2 | 4 |

2 | 2 |

1 |

Factors of 12 = 2 x 2 x 3

Factors of 16 = 2 x 2 x 2 x 2

Multiply all the common factors of 12 and 16.

2 x 2 = 4

GCF(12, 16) = 4

19

Find the GCF of 6 and 9

3 is the GCF of 6 and 9

Factors of 6

2 | 6 |

3 | 3 |

1 |

Factors of 9

3 | 9 |

3 | 3 |

1 |

Factors of 6 = 2 x 3

Factors of 9 = 3 x 3

Multiply all the common factors of 6 and 9.

3 = 3

GCF(6, 9) = 3

20

Find the GCF of 24 and 36

12 is the GCF of 24 and 36

Factors of 24

2 | 24 |

2 | 12 |

2 | 6 |

3 | 3 |

1 |

Factors of 36

2 | 36 |

2 | 18 |

3 | 9 |

3 | 3 |

1 |

Factors of 24 = 2 x 2 x 2 x 3

Factors of 36 = 2 x 2 x 3 x 3

Multiply all the common factors of 24 and 36.

2 x 2 x 3 = 12

GCF(24, 36) = 12