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Published byCarmella George Modified over 9 years ago

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**Used to find the LCM and GCF to help us add and subtract fractions.**

Prime Factorization Used to find the LCM and GCF to help us add and subtract fractions.

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Factors A factor is a number that divides another number with no remainder. Examples: factors of 12 are 1 & 12, 2 & 6, 3 & 4

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**Prime numbers A number that has only two factors, 1 and itself.**

Examples: 2, 3, 5, 7, 11, 13, 17…

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Prime Factorization The prime factorization of a number is the product of its prime factors. Example: of 12- or

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Factor Trees Use a factor tree to break down a number to get to the prime numbers (till you can’t break it down anymore) or

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Another example

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One more example…

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Now you try … Find the prime factorization of: 40 48

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GCF The Greatest Common Factor between at least two numbers… used to simplify fractions.

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GCF The greatest common factor of two or more numbers is the greatest factor that is in common to those numbers. The GCF can be found by: Listing all the factors of each number and then finding the largest number in all lists to give the GCF. Do a factor tree of each number and the prime factors that are in all trees multiply to give the GCF.

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**Listing all the factors…**

This works best when the numbers are small and have few factors. 12 and 15 Factors of 12: 1, 2, 3, 4, 6, 12 Factors of 15: 1, 3, 5, 15 GCF= 3

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Do a factor tree… This works best when the numbers are large and have many factors. These two trees share a 3 and 5. Multiply these two together and get 15. GCF=15

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**Try another with a factor tree**

45 and 81 GCF=3x3=9

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**Now you try… Find the GCF**

16 and 24 12, 48, 72

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LCM Least Common Multiple between at least two numbers… used to find a common denominator to help add and subtract fractions.

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Multiple The multiple of a number is a product of that number and a whole number… Meaning multiply! Multiples of 5: 5, 10, 15, 20, 25, 30… Multiples of 3: 3, 6, 9, 12, 15, 18, 21…

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LCM Least Common Multiple is the smallest multiple of two or more numbers. The easiest way to find the LCM: Start to list all the multiples of the numbers involved and stop as soon as you have a number in common to both lists. Ex: between 3 and 5 5, 10, 15, 20… 3, 6, 9, 12, 15… So the LCM is 15!

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**You try it! Find the LCM between 4 and 9**

Make a list of multiples of each number. 4, 8, 12, 16, 20, 24, 28, 32, 36, 40 9, 18, 27, 36.. LCM = 36!

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