Lesson plan

# 8. Multiply to find the area of rectangles and explore the commutative property (FP)

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.Content.3.OA.B.5 http://corestandards.org/Math/Content/3/OA/B/5
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

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Lesson objective: Use multiplication to find the area of a rectangle and explain why tiling a rectangle with unit squares is equivalent to multiplying the side lengths. Use area models to explain the commutative property of multiplication.

This lesson helps to build procedural skill with multiplying side lengths to find the area of a rectangle. Partitioning the rectangle into equal-sized square units, skip counting, and repeated addition are used here because it supports students' understanding of the concept of area and the structure of multiplication, and promotes understanding of the commutative property. This work develops students' understanding that we can find the area of a rectangle (with whole nimber side lengths) by tiling it with unit squares or by multiplying the side lengths.

Students engage in Mathematical Practice 6 (attend to precision) as they express their understanding of the connection between area of a rectangle and multiplication. Students also engage in Mathematical Practice 7 (look for and make use of structure) as they explore the commutative property of multiplication using rectangular array area models.

Key vocabulary:

• area
• array
• equal groups
• factors
• multiply
• partition
• product
• property of multiplication
• related multiplication equation
• repeated addition equation
• rows of
• side lengths
• skip count
• square unit
• tiling
• unit square

Special materials needed: (optional)

• centimeter graph paper
• square tiles