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4-2 6 th grade math Prime Factorization

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Objective To use divisibility rules to check for divisibility and write the prime factorization of numbers in exponential form. Why? To help you with prime factoring, simplifying fractions, division.

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California State Standards NS 1.4 (Gr. 5): Determine the prime factors of all numbers through 50 and write the numbers as the product of their prime factors by using exponents to show the multiples (e.g., 24 = 2 x 2 x 2 x 3 = 2 ³ x 3) MR 3.3: Develop generalizations of the results obtained and the strategies used and apply them in new problem situations.

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Vocabulary Divisible – A number is divisible by another number if the remainder is zero after dividing. 36 ÷ 6 = 6 Prime Number – A whole number greater than one with only two factors- itself and one. 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 57, 59, … Composite Number – A whole number greater than one that has more than two factors 4, 6, 8, 9, 10, 12, 14, 15, 16, 18, 20, 21, 22, 24, 25, 26, 27, 28, … Prime Factorization – Writing a number as the product of its prime factors 24 = 2 x 2 x 2 x 3

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Divisibility Rules! Divisibility Rules A number is divisible by: 2If the last digit ends in 0, 2, 4, 6, 8 (any even number) 3If the sums of the digits is divisible by 3 (may be even or odd) 4If the last two digits are divisible by 4 (only an even number) 5If the last digit ends in 0 or 5 (any number ending in 5 or 0) 6If the number is divisible by 2 and 3 (only an even number) 9If the sum of the digits is divisible by 9 (may be even or odd) 10If the last digit ends with a 0 (only ends in 0)

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How To Prime Factor - #1 Make a ‘Factor Tree’ 40 2 x 20 5 x 4 2 x 2 = 2 ³ x 5 Factor out each number until you get only primes Circle the prime numbers to be organized Put final answer in exponential form

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How to Prime Factor- #2 Make a ‘Factor Ladder’ Put the number at the top of a ‘ladder’= box If it is even, begin ÷ 2 If not, try greater primes like 3, 5, 7, 9 Only move on when the current number you are using doesn’t work anymore Use the divisibility rules to help The numbers on the side of the ladder are the numbers used for prime factorization. prime factor 40 = 2 ³ x 5 40 220 210 25

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Try It! Tell if each number is divisible by: 2, 3, 4, 5, 6, 9,or 10 1)3,742 2)5,310 3)47,388 4)9,999 5)41, 112 1)2 2)2, 3, 5, 6, 9, 10 3)2, 3, 4, 6 4)3, 9 5) 2, 3, 4, 6, 9

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Try Some More! Use exponents to write the prime factorization of each number. 1)64 2)48 3)76 1) 64= 2 ⁶ 2) 48 = 2 ⁴ x 3 64 232 216 28 24 22 48 224 212 26 23 3) 76 = 2² x 19 76 238 219

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More to Try Prime factor using exponents. 9)81 10) 90 9) 81 = 3⁴ 10) 90 = 2 x 3 ² x 5 81 99 3x3 90 910 3 x 35 x 2

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Objective Review To use divisibility rules to check for divisibility and write the prime factorization of numbers in exponential form. Why? You can now prime factor efficiently, simplify fractions, and divide better

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Independent Practice Complete problems 12- 23 Copy original problem first. Show all work! If time, complete Mixed Review: 24-29 If still more time, work on Accelerated Math.

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