Module 9 Lesson 3 Perimeter of a Rectangle

Module 9: Apply Multiplication To Area

Lesson 3: Find Unknown Measures pages 227-229

We Can..................

• find the unknown measure of a rectangle given the length of one side and the area or perimeter.

• Solve problems involving unknown measures in rectangles.

• Explain how to use the area formula to find the unknown measure of a rectangle given the length of one side and the area.

• Explain how to use the perimeter formula to find the unknown measure of a rectangle given the length of one side and the perimeter.

• Solve problems about the area and perimeter of rectangles and explain reasoning.

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Perimeter

Perimeter is the distance around a two-dimensional shape.

Example: the perimeter of this rectangle is 7+3+7+3 = 20

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Multiple Choice

Problem of the Day

The perimeter of a rectangle is 20 inches. What are possible measurements for the length and width? Justify your answer.

• 2 inches and 8 inches;

  4x3+6x6=6+12=22

• 3 inches and 7 inches;

  2x3+2x7=6+14=20

• 4 inches and 6 inches;

  6x3+2x7=6+13=21

• 5 inches and 4 inches;

  5x3+2x7=6+11=23

Multiple Choice

I can find the unknown measure of a rectangle given the length of one side and the area or perimeter.

Leisl is decorating the front window of a shop with a string of lights. She uses 50 feet of lights around the window. The window is 10 feet wide. What is the length of the window?

• The window is 11 feet wide. The perimeter, or distance around the window is 40 feet.

• The window is 12 feet wide. The perimeter, or distance around the window is 30 feet.

• The window is 10 feet wide. The perimeter, or distance around the window is 50 feet.

• The window is 13 feet wide. The perimeter, or distance around the window is 60 feet.

​The length of the window is 15 feet.

Multiple Choice

Step it Out page 228

Samuel is decorating a different window in the shop. The window is a rectangle and has an area of 72 square feet. The length of the window is 9 feet. What is the width? What do you want to find out?

• the length of the window.

• the height of the window.

• the interior of the window.

• the width of the window.

​What do you know? The window is nine feet long. The window has an area of 72 square feet.

​The width of the window is eight feet.

Multiple Choice

Check Understanding

Use the area or perimeter formula to find the unknown measure.

1Elise is painting a stage set that has an area of 48 square feet. The width of the set is 6 feet. What is the length?

• 6 feet

• 7 feet

• 8 feet

• 9 feet

Multiple Choice

Check Understanding

Use the area or perimeter formula to find the unknown measure.

Jada has 38 yards of fencing to put around a paddock for some goats. She has the length set as 10 yards. What is the width of the paddock?

• 6 yards

• 9 yards

• 7 yards

• 8 yards

On Your Own​

Complete page 229 in your math workbook on your own.