Description: In Topic C, students begin building fluency with facts of 2 and 3 using the array model and familiar skip-counting strategies. Lessons 7 and 8 introduce the new complexity of manipulating arrays to study the commutative property. Students learn to distinguish rows from columns as they rotate arrays 90 degrees, noticing that the meaning of the factors changes depending on the orientation of the array. Lessons 9 and 10 introduce the distributive property as a strategy for multiplication. In Lesson 9, students use arrays to decompose unknown facts as the sum or difference of two known facts. In Lesson 10, students learn to write the decomposition as (5 × 3) + (2 × 3) = 21.

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