Transcript Welcome to Math Class!

Welcome to Math
Class!
Today we are learning about:
Least Common Multiples
Materials you will need
for class:
•
•
•
•
Math journal
Math textbook
Pencil
Eraser
Your desk should be cleared
except for these four things!
I scream for ice-cream!
Sally knows that the ice-cream truck
drives by her house every 3 days. On
what days can she plan to buy icecream from the ice-cream truck?
Solution Example:
Multiply a whole number by counting numbers…
3x1=3
3x2=6
3x3=9
3 x 4 = 12
3 x 5 = 15
3 x 6 = 18
The ice-cream truck will come by on days 3, 6, 9, 12,
15, and 18. On what other days will the ice-cream
truck come by?
Now you try!
Get ready to work with your small group
to try some examples. Ready…set…GO!
We all scream for
ice-cream!
Sally wants to know more information!
We already know that the ice-cream
truck comes by every 3 days.
However, there is another ice-cream
truck that drives by Sally’s house
every 4 days. When is the next time
that both ice-cream trucks will drive
by on the same day?
What is our first step?
We need to figure out the days that
the 1st ice-cream truck will drive by
Sally’s house by identifying multiples
of 3. We already did this! How did we
solve this part of the problem?
Show our work!
3x1=3
3x2=6
3x3=9
3 x 4 = 12
3 x 5 = 15
3 x 6 = 18
3 x 7 = 21
3 x 8 = 24
3 x 9 = 27
3 x 10 = 30
The first ice-cream truck will come by on days 3, 6, 9, 12, 15, 18, 21,
24, 27, and 30.
What is our second step?
We need to figure out what days the
2nd ice-cream truck will drive by
Sally’s house by identifying multiples
of 4. How do we do this?
Show our work!
4x1=4
4x2=8
4 x 3 = 12
4 x 4 = 16
4 x 5 = 20
4 x 6 = 24
4 x 7 = 28
4 x 8 = 32
4 x 9 = 36
4 x 10 = 40
The second ice-cream truck will come by on days 4, 8, 12, 16, 20, 24,
38, 32, 36, and 40.
What is our next step?
We need to figure out the common
multiples, or the days when both icecream trucks will drive by Sally’s
house. How do we do this?
Show our work!
Let’s compare the schedule for both ice-cream
trucks. On what days will both trucks drive by
Sally’s house?
Ice-cream truck #1:
Ice-cream truck #2:
3x1=3
3x2=6
3x3=9
3 x 4 = 12
3 x 5 = 15
3 x 6 = 18
3 x 7 = 21
3 x 8 = 24
3 x 9 = 27
3 x 10 = 30
4x1=4
4x2=8
4 x 3 = 12
4 x 4 = 16
4 x 5 = 20
4 x 6 = 24
4 x 7 = 28
4 x 8 = 32
4 x 9 = 36
4 x 10 = 40
What is our last step?
We figured out the days when both
ice-cream trucks will drive by Sally’s
house, but we’re not done yet! Sally
said she wanted to know the next
time both trucks will drive by. When
will that be? How do we figure this
out?
Show our work!
We know that both ice-cream trucks
will drive by Sally’s house on days 12
and 24. The smallest number is 12.
The next time both ice-cream trucks
will drive by Sally’s house is on day
12! Great job!
Least Common Multiple
• We just figured out the
least common multiple to
solve Sally’s problem!
• The least common multiple (or LCM)
is the smallest factor that two whole
numbers have in common.
Example #1 – Let’s work
together to find the LCM
for the numbers 2 and 5.
How should we set up this problem to
solve it?
Show our work!
2x1=2
2x2=3
2x3=6
2x4=8
2 x 5 = 10
2 x 6 = 12
2 x 7 = 14
2 x 8 = 16
2 x 9 = 18
2 x 10 = 20
5x1=5
5 x 2 = 10
5 x 3 = 15
5 x 4 = 20
5 x 5 = 25
5 x 6 = 30
5 x 7 = 35
5 x 8 = 40
5 x 9 = 45
5 x 10 = 50
What are the common multiples of 2 and 5?
What is the LCM?
Example #2 – Let’s work
together to find the LCM
for the numbers 10 and
4.
How should we set up this problem to
solve it?
Show our work!
10 x 1 = 10
10 x 2 = 20
10 x 3 = 30
10 x 4 = 40
10 x 5 = 50
10 x 6 = 60
10 x 7 = 70
10 x 8 = 80
10 x 9 = 90
10 x 10 = 100
4x1=4
4x2=8
4 x 3 = 12
4 x 4 = 16
4 x 5 = 20
4 x 6 = 24
4 x 7 = 28
4 x 8 = 32
4 x 9 = 36
4 x 10 = 40
What are the common multiples of 10 and
4? What is the LCM?
Turn to page 153 in
your textbook
Let’s take a look at some different ways
that we can solve problems involving
multiples.
LCM Calculator
http://www.mathsisfun.com/leastcommon-multiple-tool.html
Let’s predict what the LCM will be
when we use an LCM calculator!
Let’s play a game!
Find your math partner and get ready to play Tic-TacToe with least common multiples. One person from
each group needs to get a blank game sheet and one
deck of cards from the activities bin.
Review
• What is a multiple?
• What is one way that we can find
multiples of a whole number?
• What is a least common multiple?
• How do we figure out the least
common multiple for two whole
numbers?
HOMEWORK
Complete the LCM worksheet. Remember
to show your work for all problems.