The document provides instructions for finding the least common multiple (LCM) of two numbers. It defines key terms like multiple, common multiple, and least common multiple. It explains how to find the common multiples of two numbers by listing out their individual multiples and seeing which numbers are shared between the lists. It also introduces using prime factorizations to calculate the LCM by finding the common prime factors between the two numbers and multiplying all of the factors.

1. 5.4 Least Common Multiple
Objective: Find the least common multiple .
Image: 'So many ducks...'
www.flickr.com/photos/43078695@N00/298160420
Mr. Williams
GESD
jwilliams@gesd40.org
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2. Vocabulary
Multiple ­ the product of the number and any non zero whole number.
Common Multiple ­ a multiple shared by two or more numbers.
Least Common Multiple (LCM) ­ the smallest common multiple of two numbers.
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3. Multiples (Multiply) Skip Counting
Multiples of:
5: 5, 10, 15, 20, 25, 30, 35...
8: 8, 16, 24, 32, 40, 48, 56...
12: 12, 24, ___, ___, ___, ___...
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4. Common Multiples are just shared multiples. Numbers that
both sets have in common.
2: 2, 4, 6, 8, 10 , 12, 14, 16, 18, 20 , 22, 24, 26, 28, 30 ...
5: 5, 10 , 15, 20 , 25, 30 ...
Common Multiples: 10, 20, 30...
The Least Common Multiple is just the smallest of the
common multiples. So the LCM of 2 and 5 is 10.
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5. Finding LCM using Prime Factors
42 60
10 6
6 7
2 5 2 3
2 3
PF = 2 x 3 x 7 PF = 2 x 2 x 3 x 5
PF = 2 x 3 x 7
PF = 2 x 2 x 3 x 5
LCM = 2 x 2 x 3 x 5 x 7
LCM = 420
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6. Video Review
http://www.unitedstreaming.com/videos/11438/sec11923_256k.asf
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