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
