Transcript least common multiple - Kyrene School District

5-5 Least Common Multiple
Warm Up
Problem of the Day
Lesson Presentation
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5-5 Least Common Multiple
Warm Up
Write the first five multiples of each
number.
1. 5
5, 10, 15, 20, 25
2. 6
6, 12, 18, 24, 30
3. 10
10, 20, 30, 40, 50
4. 12
12, 24, 36, 48, 60
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5-5 Least Common Multiple
Problem of the Day
Greg, Sam and Mary all work at the same
high school. One of them is a principal, one
of them is a teacher, and one of them is a
janitor. Sam is older than Mary. Mary does
not live in the same town as the principal.
The teacher, the oldest of the three, often
plays golf with Greg. What is each person’s
job.
Greg, principal; Sam, teacher; Mary, janitor
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5-5 Least Common Multiple
Learn to find the least common multiple
(LCM) of a group of numbers.
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5-5 Least
InsertCommon
Lesson Title
Here
Multiple
Vocabulary
least common multiple (LCM)
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5-5 Least Common Multiple
Additional Example 1: Consumer Application
English muffins come in packs of 8, and eggs in cartons of 12.
If there are 24 students, what is the least number of packs and
cartons needed so that each student has a muffin sandwich
with one egg and there are no muffins left over?
Draw muffins in groups of 8. Draw eggs in groups of 12.
Stop when you have drawn the same number of each.
There are 24 English muffins and 24 eggs.
So 3 packs of English muffins and 2 cartons of eggs are
needed.
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5-5 Least Common Multiple
Try This: Example 1
Dog cookies come in packages of 6, and bones in bags of 9. If
there are 18 dogs, what is the least number of packages and
bags needed so that each dog has a treat box with one bone
and one cookie and there are no bones or cookies left over?
Draw cookies in groups of 6. Draw bones in groups of 9. Stop
when you have drawn the same number of each.
There are 18 dog cookies and 18 bones.
So 3 packages of dog cookies and 2 bags of bones are needed.
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5-5 Least Common Multiple
The smallest number that is a
multiple of two or more numbers is
the least common multiple (LCM).
In Additional Example 1, the LCM of 8
and 12 is 24.
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5-5 Least Common Multiple
Additional Example 2A: Using Multiples to Find
the LCM
Find the least common multiple (LCM).
Method 1: Use a number line.
A. 3 and 4
Use a number line to skip count by 3 and 4.
0
2
4
6
8
10
The least common multiple (LCM) of 3 and 4 is 12.
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12
5-5 Least Common Multiple
Additional Example 2B: Using Multiples to Find
the LCM
Find the least common multiple (LCM).
Method 2: Use a list.
B. 4, 5, and 8
4: 4, 8, 12 , 16, 20, 24, 28, 32,
36, 40, 44, . . .
List multiples of 4, 5, and 8.
5: 5, 10, 15, 20, 25, 30, 35, 40,
45, . . .
8: 8, 16, 24, 32, 40, 48, . . .
LCM: 40
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Find the smallest number
that is in all the lists.
5-5 Least Common Multiple
Remember!
The prime factorization of a number is the
number written as a product of its prime
factorization.
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5-5 Least Common Multiple
Additional Example 2C: Using Multiples to Find
the LCM
Find the least common multiple (LCM).
Method 3: Use prime factorization.
C. 6 and 20
6=2•3
20 = 2
•2•5
Write the prime factorization of
each number.
Line up the common factors.
2•3 •2•5
To find the LCM, multiply one
2 • 3 • 2 • 5 = 60 number from each column.
LCM: 60
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5-5 Least Common Multiple
Additional Example 2D: Using Multiples to Find
the LCM
Find the least common multiple (LCM).
D. 15, 6, and 4
15 = 3 • 5
Write the prime factorization of
each number in exponential form.
6=3•
2
4=
22
2
3•5•2
2
3 • 5 • 2 = 60
LCM: 60
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To find the LCM, multiply each
prime factor once with the
greatest exponent used in any of
the prime factorizations.
5-5 Least Common Multiple
Try This: Example 2A
Find the least common multiple (LCM).
Method 1: Use a number line.
A. 2 and 3
Use a number line to skip count by 2 and 3.
0
1
2
3
4
5
The least common multiple (LCM) of 2 and 3 is 6.
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6
5-5 Least Common Multiple
Try This: Example 2B
Find the least common multiple (LCM).
Method 2: Use a list.
B. 3, 4, and 9
3: 3, 6, 9, 12, 15, 18, 21, 24,
27, 30, 33, 36, . . .
List multiples of 3, 4, and 9.
4: 4, 8, 12, 16, 20, 24, 28, 32,
36, …
Find the smallest number
that is in all the lists.
9: 9, 18, 27, 36, 45, . . .
The least common multiple of 3, 4, and 9 is 36.
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5-5 Least Common Multiple
Try This: Example 2C
Find the least common multiple (LCM).
Method 3: Use prime factorization.
C. 4 and 10
4=2•2
10 = 2
•5
Write the prime factorization of
each number.
Line up the common factors.
2•2 •5
2 • 2 • 5 = 20
LCM: 20
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To find the LCM, multiply one
number from each column.
5-5 Least Common Multiple
Try This: Example 2D
Find the least common multiple (LCM).
D. 12, 6, and 8
12 = 22 • 3
6=2• 3
Write the prime factorization of
each number in exponential form.
8 = 23
23 • 3
23 • 3 = 24
LCM: 24
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To find the LCM, multiply each
prime factor once with the
greatest exponent used in any of
the prime factorizations.
5-5 Least Common Multiple
Lesson Quiz
Find the least common multiple (LCM).
1. 6, 14 42
2. 9, 12 36
3. 5, 6, 10 30
4. 12, 16, 24, 36 144
5. Two students in Mrs. Albring’s preschool class
are stacking blocks, one on top of the other.
Reece’s blocks are 4 cm high and Maddy’s blocks
are 9 cm high. How tall will their stacks be when
they are the same height for the first time?
36 cm
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