Finding the GCF

I can find the GCF of two whole numbers less than or equal to

100.

What is a GCF?

The Greatest Common Factor (G.C.F.) of two

numbers is the largest number that is a divisor

of both. It can be used to simplify (or reduce)

fractions.

What is a GCF?

GREATEST is biggest or largest.

COMMON is something shared or in common.

FACTORS are the parts of multiplication facts.

What is a GCF? There are multiple ways to

find the GCF

Today we will talk about two of the following two methods:

1) The Tree Method (Prime Factorization)

2) Listing Method

Tree Method 1) Break the number down until

it is only prime numbers 2)  List the number as a

factor of primes 3)  Find all the prime numbers

the two original number share

4)  Multiply. The product is the greatest common

factor

Tree Method Break each number down to prime

factors. 56 84

2 28 2 14 2 7

42

2

2

7 6

3

Prime Factorization of 56 and 84

56: 2x2x2x7 84: 2x2x7x3

Multiply only one row. 2x2x7

The GCF is 28

Circle what they have in

common

Tree Method Break each number down to prime

factors. 63 81

7 9 3 3

9 9

3 3 3 3

Prime Factorization of 63 and 81

63:3X3x7 81:3x3x3x3

Multiply only one row. 3x3

The GCF is 9

Circle what they have in

common

Tree Method

   48 56                                

6 8

4 2 3 2

2 2

8 7

4 2

2 2

48  :  2  x  2  x  2  x  2  x  3  56:  2  x  2  x  2  x  7    

2 x 2 x 2 = 6 GCF = 6

Tree Method

   24 36                                

6 3

3 2

9

3 3 2 2

24  :  2  x  3  x  3  36  :  2  x  2  x  3  x  3    2 x 3= 6

GCF = 6

4

Now try example 5 through 8 using the

tree method by yourself!

Exit

Sli

p

Finding the GCF Activity

I can find the GCF of two whole numbers less than or equal to

100.

Find the GCF of the following numbers

26 and 42

Find the GCF of the following numbers

30 and 40

Find the GCF of the following numbers

32 and 44

Find the GCF of the following numbers

27 and 45

Find the GCF of the following numbers

36 and 48

Find the GCF of the following numbers

65 and 91

Find the GCF of the following numbers

84 and 92

Find the GCF of the following numbers

51 and 75

Find the GCF of the following numbers

64 and 72

Find the GCF of the following numbers

99 and 66

Find the GCF of the following numbers

20 and 24

Find the GCF of the following numbers

21 and 56

Find the GCF of the following numbers

18 and 90

Find the GCF of the following numbers

8 and 64

Find the GCF of the following numbers

20 and 45

Find the GCF of the following numbers

18 and 63

Find the GCF of the following numbers

42 and 48

Find the GCF of the following numbers

16 and 28

Find the GCF of the following numbers

30 and 42

Find the GCF of the following numbers

36 and 72

Find the GCF of the following numbers

15 and 40

Find the GCF of the following numbers

24 and 28

Find the GCF of the following numbers

24 and 32

Find the GCF of the following numbers

9 and 54

Find the GCF of the following numbers

40 and 50

Find the GCF of the following numbers

6 and 36