Objective - To find the Least Common Multiple (LCM) of two whole numbers.

Smallestnumber that a set of given numbers dividesevenly into.

LCM - Least Common Multiple -

Two ways to find the LCM1) Make a list of multiples.

2) Use the prime factorizations to selectthe common factors once plus all theremaining factors.

GCF vs. LCM

GCF

16 20

= 4

LCM = 80

GCF - Reduce or Simplify

1620

4÷4÷

45=

LCM- Compare, Add, or Subtract5 7 16 20

80 80

( )55

25 28

( )44

Make a list of the multiples less than 50 and circle the common multiples.

1) 6, 86: 6, 12, 18, 24, 30, 36, 42, 48

8: 8, 16, 24, 32, 40, 48

2) 4, 12

4: 4, 8 , 12, 16, 20, 24, 28, 32

12: 12 , 24 , 36 , 48

, 36, 40, 44, 48

Make a list of the first eight multiples and circle the LCM.

1) 3, 73: 3, 6 , 9 , 12, 15, 18, 21, 24

7: 7, 14, 21, 28, 35, 42, 49, 56

2) 2, 4,16

2: 2, 4 , 6 , 8 , 10, 12, 14, 16

16: 16, 32, 48, 64

4: 4, 8 , 12, 16, 20, 24, 28, 32

, 80, 96, 112 , 128

Use prime factorization to find the LCM.21

3 7

3 7

18

2 9

3 3

2 3 3 3 7•2 3 3• •

Select all common factors once.

LCM = 3Then select the remaining factors.

2• 3• 7•LCM 126=

Use prime factorization to find the LCM.45

5 9

3 3

48

8 6

2 32 4

2 22 2 2 2 3• • • •3 3 5• •

Select all common factors once.

LCM = 3Then select the remaining factors.

3• 5• 2• 2•LCM 720=

2• 2•

Lesson 3-3

Math 6 Slide Show: Teaching Made Easy As Pi, by Mike Mills and James Wenk © 2011

Use prime factorization to find the LCM.16

2 8

2 4

30

2 15

3 5

2 2

20

2 10

2 5

2 3 5• •2 2 2 2• • •

Select all common factors once.

LCM = 2Then select the remaining factors.

2• 5• 2• 2•LCM 240=

3•

2 2 5• •

(common to all three or just two)

Use prime factorization to find the LCM.18

2 9

3 3

40

2 20

30

2 15

3 5 2 10

2 52 2 2 5• • •2 3 3• •

Select all common factors once.

LCM = 2Then select the remaining factors.

3• 5• 3• 2•LCM 360=

2•

2 3 5• •

(common to all three or just two)

Lesson 3-3 (cont.)

Math 6 Slide Show: Teaching Made Easy As Pi, by Mike Mills and James Wenk © 2011