Videos to help Grade 3 students learn how to analyze different rectangles and reason about their area.

Common Core Standards: 3.MD.5, 3.MD.6, 3.MD.7a, 3.MD.7b, 3.MD.7d

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Lesson Plans and Worksheets for Grade 3

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Common Core For Grade 3

New York State Common Core Math Module 4, Grade 3, Lesson 9

Application Problem

Mario plans to completely cover his 8-inch by 6-inch cardboard with square-inch tiles. He has 42 square-inch tiles. How many more square-inch tiles does Mario need to cover the cardboard without any gaps or overlap? Explain your answer.

Note: This problem reviews the concept of finding area. Students will likely solve by multiplying side lengths (shown above), having just practiced this strategy in 3–M4–Lesson 8.

Concept Development

How can we use the areas of 2 small rectangles that form a longer rectangle to find the area of the longer rectangle?

Add the areas of the smaller rectangles.

Lesson 9 Homework

1. Use the grid to answer the questions below.

a. Draw a line to show how to divide the grid into 2 equal rectangles. Shade in 1 of the rectangles.

b. Label the side lengths of each rectangle.

c. Write an equation to show the total area of the 2 rectangles.

2. Alexa cuts out the 2 equal rectangles from Problem 1(a) and puts the two shorter sides together.

a. Draw Alexas new rectangle and label the side lengths below.

b. Find the total area of the new, longer rectangle.

c. Is the area of the new, longer rectangle equal to the total area in Problem 1(c)? Explain why or why not.