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Preview Warm Up California Standards Lesson Presentation

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**Warm Up Write each fraction in simplest form. 4 48 1 12 9 135 1 15 2.**

1. Convert the following measurements. inches = feet 16 feet = inches 222 inches = feet 27

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California Standards NS Use proportions to solve problems (e.g., determine the value of N if T = , find the length of a side of a polygon similar to a known polygon). Use cross-multiplication as a method for solving such problems, understanding it as the multiplication of both sides of an equation by a multiplicative inverse. 4 7 N 21

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Vocabulary scale model scale factor scale scale drawing

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**This HO gauge model train is a scale model of a historic train**

This HO gauge model train is a scale model of a historic train. A scale model is a proportional model of a three-dimensional object. Its dimensions are related to the dimensions of the actual object by a ratio called the scale factor. The scale factor of an HO gauge model train is 1 87 This means that each dimension of the model is of the corresponding dimension of the actual train. 1 87

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**A scale is the ratio between two sets of measurements**

A scale is the ratio between two sets of measurements. Scales can use the same units or different units. The photograph shows a scale drawing of the model train. A scale drawing is a proportional two-dimensional drawing of an object. Both scale drawings and scale models can be smaller or larger than the objects they represent.

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**Additional Example 1: Finding a Scale Factor**

Identify the scale factor. You can use the lengths or widths to find the scale factor. Room Blueprint Length (in.) 144 18 Width (in.) 108 13.5 blueprint length room length 18 144 1 8 = = Write a ratio. Then simplify. blueprint width room width 13.5 108 1 8 = = Write a ratio. Then simplify. 1 8 The scale factor is .

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**Identify the scale factor.**

Check It Out! Example 1 Identify the scale factor. Model Aircraft Blueprint Length (in.) 12 2 Wing span (in.) 18 3 blueprint length aircraft length 2 12 1 6 = = Write a ratio. Then simplify. blueprint wing span aircraft wing span 3 18 1 6 = = Write a ratio. Then simplify. The scale factor is . 1 6

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**Additional Example 2: Using Scale Factors to Find Unknown Lengths**

A photograph was enlarged and made into a poster. The poster is 20.5 inches by 36 inches. The scale factor is . Find the size of the original photograph to the nearest tenth of an inch. 5 1 poster photo 5 1 Think: = 36 l 5 1 = Write a proportion to find the length l. 5l = 36 Find the cross products. l = 7.2 Divide.

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**Additional Example 2 Continued**

A photograph was enlarged and made into a poster. The poster is 20.5 inches by 36 inches. The scale factor is . Find the size of the photograph. 5 1 poster photo 5 1 Think: = 20.5 w 5 1 Write a proportion to find the width w. = 5w = 20.5 Find the cross products. w = 4.1 Divide. The photo is 7.2 in. long and 4.1 in. wide.

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**factor is . Find the size of the dollhouse. 1.5 1**

Check It Out! Example 2 Mary’s father made her a dollhouse which was modeled after the blueprint of their home. The blueprint is 24 inches by 45 inches. The scale factor is Find the size of the dollhouse. 1.5 1 dollhouse blueprint 1.5 1 Think: = l 45 = 1.5 1 Write a proportion to find the length l. Find the cross products. l = 45 · 1.5 l = 67.5 Multiply.

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Check It Out! 2 Continued Mary’s father made her a dollhouse which was modeled after the blueprint of their home. The blueprint is 24 inches by 45 inches. The scale factor is Find the size of the dollhouse. 1.5 1 dollhouse blueprint 1.5 1 Think: = w 24 1.5 1 Write a proportion to find the width w. = w = 24 · 1.5 Find the cross products. w = 36 Multiply. The dollhouse is 67.5 inches long and 36 inches wide.

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**Additional Example 3: Measurement Application**

On a road map with a scale of 1.5 inches = 60 miles, the distance between Pittsburgh and Philadelphia is 7.5 inches. What is the actual distance between the cities? Let d be the actual distance between the cities. 1.5 60 7.5 d = Write a proportion. 1.5 · d = 60 · 7.5 Find the cross product. 1.5d = 450 Multiply. 1.5d 1.5 450 1.5 = Divide both sides by 1.5. d = 300 The distance between the cities is 300 miles.

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Check It Out! Example 3 On a road map with a scale of 1 inch = 50 kilometers, the distance between Dallas and Houston is 7 inches. What is the actual distance between the two cities? Let d be the actual distance between the cities. 1 50 7 d = Write a proportion. 1 · d = 50 · 7 Find the cross products. 1d = 350 Multiply. d = 350 The distance between the cities is 350 kilometers.

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