Lesson plan

# 7. Understand that the area of a rectangle can be determined by multiplying side lengths (C)

teaches Common Core State Standards CCSS.Math.Content.3.MD.C.7a http://corestandards.org/Math/Content/3/MD/C/7/a
teaches Common Core State Standards CCSS.Math.Practice.MP2 http://corestandards.org/Math/Practice/MP2
teaches Common Core State Standards CCSS.Math.Practice.MP4 http://corestandards.org/Math/Practice/MP4
teaches Common Core State Standards CCSS.Math.Practice.MP6 http://corestandards.org/Math/Practice/MP6

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Lesson objective: Understand that we can find the area of a rectangle (with whole number length sides) by tiling it with unit squares or by multiplying the side lengths.

Students bring prior knowledge of using repeated addition to find the total number of objects in an array from 2.OA.C.4 and using a multiplication equation to describe an array from 3.OA.A.1. This prior knowledge is extended to using the multiplication equation: area = length x width to find the area of a rectangle as students use square tiles to create rectangular arrays (area  models) for a given number of vegetables in a vegetable plot, and write equations to represent the total number of vegetables. A conceptual challenge students may encounter is understanding and explaining why the formula length x width can be used to find the area of a rectangle.

The concept is developed through work with arrays of square tiles and repeated addition equations, which support students' understanding of the connection to multiplication.

This work helps students deepen their understanding of operations because students will connect their work with arrays and repeated addition to understand why multiplication of side lengths can be used to find the area of a rectangle.

Students engage in Mathematical Practice 2 (reason abstractly and quantitatively) as they use square tiles to represent the possible dimensions of each vegetable plot. Students will move to more abstract reasoning as they learn to write a multiplication equation to find the area of a rectangle.

Key vocabulary:

• area
• array
• equal group
• length
• multiplication equation
• rectangle