Fishtank Learning

3rd Grade Math
Unit 4: Area
Lesson 6

Objective

Find the area of a rectangle through multiplication of the side lengths.

Anchor Tasks - Problem 1

a. The tick marks on the sides of the rectangle below are 1 unit apart.

Rectangle with 5 units on top and 4 units on the side, representing area calculation.

What is the area in square units? Show or explain how you know.

b. The top side of this rectangle is marked off in unit lengths. The left side is labeled with the length in units.

Rectangle with top side marked in 3 unit lengths, left side labeled 3 units.

What is the area in square units? Show or explain how you know.

Guiding Questions

How many columns of square units are in the rectangle in Part (a)? How many rows?
How is the rectangle in Part (b) different from the rectangle in Part (a)?
How many columns of square units are in the rectangle in Part (b)? How can you figure out the number of rows in the rectangle in Part (b)?
What is the area of the rectangle in Part (a)? In Part (b)?
How are the side lengths related to the area of the rectangle?
Write a multiplication equation to represent the area of the rectangle in relation to the side lengths.

Notes

Show students the image in the Anchor Task, rather than giving students their own copy of it. This forces students to find the area by thinking about the relationship between the side length and the area without being able to draw individual square units.

Anchor Tasks - Problem 2

a. Write a multiplication expression that represents the area of the following figure. Then find its area.

Rectangle with dimensions 9 units by 4 units.

b. Frederick draws another rectangle with the same area. What might the length and width of Frederick's rectangle be?

Anchor Tasks - Problem 3

a. The area of the rectangle below is 42 square units. Find the missing side length.

Rectangle with one side labeled 6 units, other side unknown, area 42 square units.

b. Explain how you can use either multiplication or division to solve Part (a).

Problem Set

View Problem Set

Discussion of Problem Set

In what way is the area of #2(b) related to the area of #2(a)? How could you use the side lengths to help you figure out that 8 x 7 is double 4 x 7?
Which shape in #2 is a square? How do you know?
How are the rectangles in #2(a) and #5(c) similar? How are they different?
Was anyone able to tell which two tables in #7 had the same area before multiplying them? How was that possible?
Why is there a connection between a rectangle’s side lengths and its area?

Target Task - Problem 1

A rectangle has the measurements shown. Select the three ways to calculate the area of the rectangle in square units.

Rectangle with dimensions 8 units by 3 units; area calculation possible.

A. 3 × 3

B. 8 × 8

C. 3 × 8

D. 8 × 3

E. 3 + 3 + 3

F. 8 + 8 + 8

Target Task - Problem 2

Find the side length of the rectangle below.

Rectangle with one side labeled as 9 units and area of 45 square units.

Word Problem

During a school fundraiser, Habib sells 8 half-year magazine subscriptions of 6 magazines each. Habib sold 27 fewer magazines than Habib. How many magazines did Ebru sell?