Unit 3, Lesson 12# Apply the distributive property and the fact 9 = 10 - 1 as a strategy to multiply

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In this lesson, students use the distributive property to establish the 9 = 10 - 1 pattern for multiplication. They learn to think of each nines fact as a well-known tens fact minus one unit. For example, 9 × 8 = (10 - 1) × 8 = (10 × 8) - (1 × 8) = 80 - 8 = 72. Along the way, they use tape diagrams to represent their calculations.