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# How can you determine the amount of paint needed to cover the walls of your bedroom - but not the door, windows, and ceiling?

## Presentation on theme: "How can you determine the amount of paint needed to cover the walls of your bedroom - but not the door, windows, and ceiling?"— Presentation transcript:

How can you determine the amount of paint needed to cover the walls of your bedroom - but not the door, windows, and ceiling?

In this lesson you will learn how to solve real-life problems by applying your knowledge of surface area.

Let’s Review Surface area is the sum of the areas of the faces on a 3D solid.

A Common Mistake In real-life situations, sometimes we do not need to find the areas of all of the faces on a particular 3D solid. What if I need to paint my bedroom? floor and ceiling door and window

Core Lesson Katy is painting the walls of her bedroom, shown below. Katy will not paint the floor, the ceiling, or the door. Katy’s door is 3 feet x 8 feet. If one quart of paint covers 100 square feet, how many quarts will Katy need to purchase? SA = 2 (Sm. Wall) + 2 (Lg. Wall) - Door 12 feet 8 feet 10 feet = 2 (L W) + 2 (L W) - (L W) = 2 (8 10) + 2 (12 10) - (3 8) = 2 (80) + 2 (120) - (24) = 160 + 240 - 24 There are 376 square feet of wall that need to be covered, so Katy must purchase 4 quarts of paint.

In this lesson you have learned to solve real-life problems by applying your knowledge of surface area.

Guided Practice The dimensions of Bria’s camping tent are shown below. The tent is not waterproof, so Bria wants to put a tarp over it, in case it rains. The tarp will cover two of the tent’s rectangular faces. Which size tarp should she buy - the one that is 50 feet 2, 100 feet 2, or 150 feet 2. 6 feet 7 feet 5 feet 4 feet SA = 2 (Rectangle) = 2 (L W) = 2 (7 5) = 2 (35) = 70 ft 2 Bria should buy the 100 feet 2 tarp.

Extension Activities The house to the right is in need of a new roof. How many square feet of shingles must be purchased? Roofing is measured in “squares.” A square is equal to 100 square feet of roofing. How many squares must be purchased? A square costs \$65. How much will the new roofing cost? 20 feet 60 feet 7 feet

Extension Activities A website sells value rolls of wrapping paper and advertises that, “The most popular size is 25 inches by 405 inches, which can wrap approximately 175 - 200 gifts.” How many square feet of wrapping paper are on one roll? According to this website, what is the surface area of an average gift? If the roll costs \$40, about how much does it cost to wrap one gift?

Quick Quiz Renata bought a package of candy to give to her friend as a gift. The candy is shaped like a triangular prism, with the dimensions, below. She has three different sizes of wrapping paper to choose from. Which will be the best for wrapping the candy — the paper that is 80 cm 2, 130 cm 2, or 180 cm 2 ? Cereal boxes have the dimensions indicated in the illustration, to the left. The cereal box factory is about to close for the weekend, and there are just 1,000 in 2 of cardboard left. How many more cereal boxes can be produced at the factory with the remaining cardboard?

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