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Mental Math for Multiplication

Mental Math for Multiplication. Lesson 2.3. Distributive Property. A factor can be thought of as the sum of addends. Multiplying the sum by a number is the same as multiplying each addend by the number and adding the products. Examples. 8 x 24. Think of 24 as 20 + 4.

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Mental Math for Multiplication

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  1. Mental Math for Multiplication Lesson 2.3

  2. Distributive Property • A factor can be thought of as the sum of addends. Multiplying the sum by a number is the same as multiplying each addend by the number and adding the products.

  3. Examples 8 x 24 Think of 24 as 20 + 4 Then, multiply 8 by the 20 and the 4, and add the answers. (8 x 20) + (8 x 4) = 160 + 32 = 192

  4. Example 2 6 x 42 Think of 42 as + 40 2 (6 x 40) + (6 x 2) = 240 + 12 = 252

  5. Example 3 17 x 4 Think of 17 as + 10 7 (10 x 4) + (7 x 4) = 40 + 28 = 68

  6. Fill in the Missing Factors 7 x 26 = (7 x ) + (7 x 6) 20 33 x 9 = (30 x 9) + ( x 9) 3 48 15 x = (15 x 40) + (15 x 8) 6 x 84 = (6 x 80) + (6 x 4)

  7. Commutative Property Factors can be multiplied in any order. 12 x 7 = 7 x 12

  8. Associative Property Factors can be grouped in any way without changing the answer. 2 x (9 x 5) = (2 x 9) x 5 2 x 45 = 18 x 5 90 = 90

  9. Multiplicative Identity (a.k.a. Property of One) Any factor multiplied by 1 results in that same factor. 17 x 1 = 17 1 x 456 = 456 88,888 x 1 = 88,888

  10. Property of Zero Any factor multiplied by 0 results in 0. 6 x 0 = 0 0 x 146 = 0 88,888 x 0 = 0

  11. Name That Property • 36 x 0 = 0 • 14 x 5 = (10 x 5) + (4 x 5) • 15 x 1 = 15 • 3 x (9 x 2) = (3 x 9) x 2 • 89 x 78 = 78 x 89 • (4 x 20) + (4 x 8) = 4 x 28 Property of Zero Distributive Multiplicative Identity Associative Commutative Distributive

  12. Homework Time!

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