3.MD.C.7.a

Pitfalls to avoid when teaching 3.MD.C.7.a

GO!

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3.MD.C.7.a is focused on finding the area of a rectangle by tiling it and comparing tiles to multiplication number sentences.

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Students will learn and explain why multiplying the side lengths of a rectangle to calculate the area is the same as counting the number of unit squares that make up a rectangle.

5x6 = 30

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Tiling is a concrete process when students draw geometric tiles to make counting easier. Like tiling a floor, students are able to see shapes in the floor design. While this is a strategy, it is an explicit method defined by the standard. Not only will students use it, but it is the method of assessment.

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Unpack the standard

Click on the numbers below.

Ensure that students see rectangles with whole-number side lengths that stay between 1 - 99.

Find the area of a rectangle with whole-number side lengths by tiling it, and show that the area is the same as would be found by multiplying the side lengths.

Tiling can occur by placing manipulatives, shading grid paper, or by drawing squares. Students should always check their work with multiplication.

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Connections to Prior Learning

Click on the yellow index cards below to learn about how these standards connect to 3.MD.C.7.a.

3.MD.C.7.a Find the area of a rectangle with whole-number side lengths by tiling it, and show that the area is the same as would be found by multiplying the side lengths.

3.MD.C.6 Find the area of the shaded figure:

2.G.A.2

Partition a rectangle into rows and columns of same-size squares and count to find the total number of them.

2.G.A.2 Levels of thinking on an assessment that asks students to partition a rectangle:

3.OA.D.8 Solve two-step word problems using the four operations. Represent these problems using equations with a letter standing for the unknown quantity. Assess the reasonableness of answers using mental computation and estimation strategies including rounding.

3.MD.C.6

Measure areas by counting unit squares (square cm, square m, square in, square ft, and improvised units), ie)

3.MD.C.5 Recognize area as an attribute of plane figures and understand concepts of area measurement.

3.MD.C.5

Avoid pitfall #1!

The biggest pitfall when teaching this standard is neglecting precise mathematical language: words like perimeter and area. Without precise language, students may confuse the area and only calculate the area around the shape or of the area’s interior. When teaching, visually represent how to tile and how to multiply the area.

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Avoid pitfall #1!

The biggest pitfall when teaching this standard is neglecting precise mathematical language: words like perimeter and area. Without precise language, students may confuse the area and only calculate the area around the shape or of the area’s interior. When teaching, visually represent how to tile and how to multiply the area.

For example, in a problem like “What is the area of the shaded figure?” students may calculate the area by counting the white tiles outside the blue box or only counting the tiles in the interior of the shaded figure.

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Avoid pitfall #2!

Avoid the pitfall of relying on counting tiles.

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Avoid pitfall #2!

Avoid the pitfall of relying on counting tiles. While students may practice counting tiles to build conceptual understanding, they need to begin practicing with both addition and multiplication to more efficiently solve problems. Multiplication is critical to the standard.

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