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GREATESTGREATEST

COMMON COMMON

FACTORFACTOR

The Greatest Common Factor GCF of two or more numbers is the largest factor they have in common.

METHOD 1 List all the factors of each number

Find the largest common factor

METHOD 2 Divide both numbers by the same

factors – multiply all these factors

There are two different methods for finding There are two different methods for finding the GCF of a set of numbers.the GCF of a set of numbers.

Let’s take a look at both ways!!!!!

The Greatest Common Factor GCF of two or more numbers is the largest factor they have in common.

Find the GCF of 12 and 18

METHOD 1 List all the factors of each number

Find the largest common factor

Factors of 12 = 1 , 2, 3, 4, 6, 12

Factors of 18 = 1, 2, 3, 6, 9, 18

Circle the greatest factor they have in common

The Greatest Common Factor GCF is 6

The Greatest Common Factor GCF of two or more numbers is the largest factor they have in common.

Find the GCF of 12 and 18

METHOD 2 Divide both numbers by the same

factors – multiply all these factors

The Greatest Common Factor GCF is 6

12 182

6 93

2 3

2 x 3 = 6

6 x 2 =12 6 x 3 = 18 CHECK:

Find the Greatest Common Factor GCF of 24 and 36

METHOD 1

ALL FACTORS

METHOD 2

DIVISION

24 = 1, 2, 3, 4, 6, 8, 12, 24

36 = 1, 2, 3, 4, 6, 9, 12, 18, 36

Circle greatest common factor

GCF = 12

24 364

6 93

2 3

Multiply common factors

GCF = 4 x 3 = 1212 x 2 = 24

12 x 3 = 36

Check

The Greatest Common Factor GCF of two or more numbers is the largest factor they have in common.

Find the GCF of 90 and 120

METHOD 2 Repeated Division

The Greatest Common Factor GCF is 30

90 12010

9 123

3 4

10 x 3 = 30

30 x 3 = 90 30 x 4 = 120

CHECK:

The Greatest Common Factor GCF of two or more numbers is the largest factor they have in common.

Find the GCF of 14 and 20

METHOD 2 Repeated Division

The Greatest Common Factor GCF is 2

14 202

7 102

2 x 7 =14 2 x 10 = 20 CHECK:

The Greatest Common Factor GCF of two or more numbers is the largest factor they have in common.

Find the GCF of 32 and 80

METHOD 2 Repeated Division

The Greatest Common Factor GCF is 16

32 802

16 404

4 10

2 x 4 x 2 = 16

16 x 2 =32 16 x 5 = 80

2 5

2

CHECK:

The Greatest Common Factor GCF of two or more numbers is the largest factor they have in common.

Find the GCF of 77 and 15

METHOD 2 Repeated Division

The Greatest Common Factor GCF is 1

77 151

77 151

1 x 77 = 77 1 x 15 = 15 CHECK:

The Greatest Common Factor GCF of two or more numbers is the largest factor they have in common.

Find the GCF of 36, 48, and 30

METHOD 2 Repeated Division

The Greatest Common Factor GCF is 6

36 48 3022

18 24 1533

6 8 5

2 x 3 = 62 x 3 = 6

6 x 6 =36 6 x 8 = 48 6 x 5 =30

CHECK:

**ASSIGNMENT**

• Page 236 (#8-17, 37-38)Page 236 (#8-17, 37-38)

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