MJ2A
5.6 – Least Common Multiple
Bellwork
•
Add or subtract. Write your answer in
simplest form.
1. 1 + 1
10 3
2. 1 - 2
4
3
3. 6 1 - 4 1
2
5
Assignment Review
• Text p. 235 # 11 – 30
Before we begin…
• Please take out your notebook and get ready
to work…
• Today we will look at the Least Common
Multiple (LCM) of 2 or more numbers…
• For those students that do not know their
multiplication tables…knowing this will help
you when you have to convert fractions to a
common denominator
• Raise your hand if you can tell the class what
a least common multiple is…
Objective 5.6
• Students will find the least common
multiple of two or more numbers.
Least Common Multiple
• A multiple of a number is the product of that
number and a whole number.
Example:
5x0=0
5x1=5
5 x 2 = 10 etc…
• We can say that the multiples of 5 are 0, 5,
10, 15, etc…
• As the name suggests the least common
multiple of 2 or more numbers is the smallest
multiple that the numbers have in common.
Finding the LCM
•
There are a number of methods that can be
used to find the LCM.
• You can:
1. List the multiples of each number
2. Do a factor tree
3. Use the cake method
• For today’s lesson we will look at the cake
method as that is the easiest method…
Example
• Find the LCM of 4 and 6
2 4, 6
2 3
• The LCM will be 2x2x3 = 12
• Notice that the numbers form the shape
of an L to help you remember what to
multiply
Example
• Find the LCM of 16 & 24
2
2
2
16, 24
8 12
4 6
2 3
• The LCM is 2 x 2 x 2 x 2 x 3 = 48
How does this help with Common
Denominators?
• Knowing the LCM can help you with finding a
common denominator when adding or
subtracting unlike fractions
• In the previous example suppose you were
adding 8/16 & 3/24, you could use the cake
method to find the LCM and therefore, know
that the smallest number that both 16 and 24
go into is 48
• When using the LCM you minimize the need
to simplify the fractions
Your Turn
•
In the notes section of your notebook
write and find the LCM of the
following:
1. 6 & 8
2. 12 & 30
3. 10 & 14
LCM of Monomials
• You can also use the cake method to
find the LCM of algebraic monomials
• Find the LCM of 12b2 & 8ab
2b 12b2, 8ab
2
6b 4a
3b 2a
• The LCM = 2b x 2 x 3b x 2a = 24ab2
Your Turn
•
In the notes section of your notebook
write the monomials and then find the
LCM of each
1. 12x2y2 & 6y3
2. 15b2 & 25b3
Summary
• In the notes section of your notebook
summarize the key concepts covered in
today’s lesson.
• Today we discussed
• LCM – what is it?
• Name 3 methods to find the LCM
• How can knowing LCM help you with
unlike fractions?
Assignment
• Practice Skills workbook lesson 5.6
Reminder
•
•
•
•
This assignment is due tomorrow
I do not accept late assignments
Do the odd problems only
Write them on a separate sheet of paper
and show how you got your answer (no
work = no credit)