Transcript LCM (least common multiple)

Quote of the Day:
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Fact: Thomas Edison invented over 1000
inventions besides the light bulb
Facts about Thomas Edison
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Fact: Thomas Edison did look at it at
1000 failures before the light bulb was
invented instead…..he looked at it as
1000 ways the light bulb did not work.
Could you continue with a that kind of
positive attitude?
Math is not about perfection…its about
continuing on until accuracy is obtained.
LCM
(least common multiple)
Created by
Ms. Layne
Review Common Multiple
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A common multiple is a number that is a multiple
of two or more numbers. What are the common
multiples of 3 and 4?
Hint: Remember a multiple must start with
the number and expand or grow bigger
(a multiple can never ever be smaller than the
original number)
Multiples of 3 – 3, 6, 9, 12, 15, 18, 21, 24
Multiples of 4 – 4, 8, 12, 16, 20, 24
Therefore the common multiples of 3 and 4
are…. 12 and 24
LCM
Least Common Multiple
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Definition
The least common multiple (LCM) of two
numbers is the smallest number that is a
multiple of both.
Let’s look at our example of common
multiples of 3 and 4….
12 and 24 – What is the least common
multiple?
The LCM of 3 and 4 is 12.
3 Methods of LCM
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1. Multiples – Old School Way
2. Factor Tree – using a factor tree to
determine the LCM
3. The upside down birthday cake – the
upside down cake returns to show us
an easy way to determine the LCM
Method 1 - Multiples
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1. Write out the long way multiples of each
number.
Remember to start each number with itself than
continue on (look at a multiplication table it is
multiples of that number.
For video help please go to study jams:
http://studyjams.scholastic.com/studyjams/j
ams/math/fractions/least-commonmultiple.htm
Example will be done in class using 6 and 8.
Method 1 - Multiples
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More Examples
Method 2 – Factor Tree
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2. Factor Trees
1. make a factor tree using 6 and 8.
 2. Write out horizontal the prime factors in each number.
 3. Circle the numbers they have in common and only use
them once.
 4. Rewrite all prime factors of both numbers only using
the common numbers once.
 5. Multiply them all together to get the LCM.
 For video help see study jams:
http://studyjams.scholastic.com/studyjams/jams/math/fr
actions/least-common-multiple.htm
Example in class will be done using same numbers 6
and 8.
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Method 2 – Factor Tree
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More Examples
Method 3 – Upside Down
Birthday Cake
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3. Upside Down Birthday Cake
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1. Write the numbers in tier 1 of the cake.
2. pull out the smallest prime number.
3. Repeat each tier until you can not take out a common
prime number.
4. Multiply the prime numbers on the left like GCF and
the numbers at the bottom on the cake to get the LCM
For Video help see YouTube:
http://www.youtube.com/watch?v=GD5jLpSsN00
Example in class will be done using same example
numbers 6 and 8.
Method 3 – Upside Down
Birthday Cake
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More Examples
Thanks for stopping by
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Let’s do some examples using our
assignment problems.
Remember all power points are posted
on my website.
This homework assignment can be
found on my website also.
Have a Blessed day