EXAMPLE 3 Use a ratio of areas Cooking

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Presentation transcript:

EXAMPLE 3 Use a ratio of areas Cooking A large rectangular baking pan is 15 inches long and 10 inches wide. A smaller pan is similar to the large pan. The area of the smaller pan is 96 square inches. Find the width of the smaller pan. SOLUTION First draw a diagram to represent the problem. Label dimensions and areas. Then use Theorem 11.7. If the area ratio is a2:b2, then the length ratio is a:b.

EXAMPLE 3 Use a ratio of areas Area of smaller pan Area of large pan = 150 96 = 25 16 Write ratio of known areas. Then simplify. Length in smaller pan Length in large pan = 4 5 Find square root of area ratio. ANSWER Any length in the smaller pan is , or 0.8, of the corresponding length in the large pan. So, the width of the smaller pan is 0.8(10 inches) 8 inches. 4 5 =

EXAMPLE 4 Solve a multi-step problem Gazebo The floor of a gazebo is a regular octagon. Each side of the floor is 8 feet, and the area is about 309 square feet. You build a small model gazebo in the shape of a regular octagon. The perimeter of the floor of the model gazebo is 24 inches. Find the area of the floor of the model gazebo to the nearest tenth of a square inch.

EXAMPLE 4 Solve a multi-step problem SOLUTION All regular octagons are similar, so the floor of the model is similar to the floor of the full-sized gazebo. STEP 1 Find the ratio of the lengths of the two floors by finding the ratio of the perimeters. Use the same units for both lengths in the ratio. Perimeter of full-sized Perimeter of model = 8(8 ft) 24 in. = 64 ft 2 ft = 32 1 So, the ratio of corresponding lengths (full-sized to model) is 32:1.

Solve a multi-step problem EXAMPLE 4 Solve a multi-step problem STEP 2 Calculate the area of the model gazebo’s floor. Let x be this area. (Length of full-sized)2 (Length of model)2 Area of full-sized Area of model = Theorem 11.7 309 ft2 x ft2 322 12 = Substitute. 1024x 309 = Cross Products Property x ≈ 0.302 ft2 Solve for x.

EXAMPLE 4 Solve a multi-step problem STEP 3 Convert the area to square inches. 0.302 ft2 144 in.2 1 ft.2 ≈ 43.5 in.2 The area of the floor of the model gazebo is about 43.5 square inches. ANSWER

√ GUIDED PRACTICE for Examples 3 and 4 2. The ratio of the areas of two regular decagons is 20:36. What is the ratio of their corresponding side lengths in simplest radical form? ANSWER 5 3 √

GUIDED PRACTICE for Examples 3 and 4 3. Rectangles I and II are similar. The perimeter of Rectangle I is 66 inches. Rectangle II is 35 feet long and 20 feet wide. Show the steps you would use to find the ratio of the areas and then find the area of Rectangle I. 66 1320 = 1 20 400 is the ratio of sides, so the ratio of areas is , 252 in.2 ANSWER