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Using Ratios and Scale Drawings in Geometry: Lesson and Quiz

Learn how to make indirect measurements using ratios and scale drawings. Practice finding perimeters and areas of polygons. Quiz included.

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Using Ratios and Scale Drawings in Geometry: Lesson and Quiz

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  1. 7-5 Using Proportional Relationships Warm Up Lesson Presentation Lesson Quiz Holt Geometry

  2. Do Now Convert each measurement. 1.6 ft 3 in. to inches 2. 5 m 38 cm to centimeters Find the perimeter and area of each polygon. 3. square with side length 13 cm 4. rectangle with length 5.8 m and width 2.5 m

  3. Objectives TSW use ratios to make indirect measurements. TSW Use scale drawings to solve problems.

  4. Indirect measurementis any method that uses formulas, similar figures, and/or proportions to measure an object. The following example shows one indirect measurement technique.

  5. Helpful Hint Whenever dimensions are given in both feet and inches, you must convert them to either feet or inches before doing any calculations.

  6. Example 1: Measurement Application Tyler wants to find the height of a telephone pole. He measured the pole’s shadow and his own shadow and then made a diagram. What is the height h of the pole?

  7. Example 2 A student who is 5 ft 6 in. tall measured shadows to find the height LM of a flagpole. What is LM?

  8. A scale drawingrepresents an object as smaller than or larger than its actual size. The drawing’s scaleis the ratio of any length in the drawing to the corresponding actual length. For example, on a map with a scale of 1 cm : 1500 m, one centimeter on the map represents 1500 m in actual distance.

  9. Remember! A proportion may compare measurements that have different units.

  10. On a Wisconsin road map, Kristin measured a distance of 11 in. from Madison to Wausau. The scale of this map is 1 inch:13 miles. What is the actual distance between Madison and Wausau to the nearest mile? Example 3: Solving for a Dimension

  11. Example 4 Find the actual distance between City Hall and El Centro College.

  12. Example 5: Making a Scale Drawing Lady Liberty holds a tablet in her left hand. The tablet is 7.19 m long and 4.14 m wide. If you made a scale drawing using the scale 1 cm:0.75 m, what would be the dimensions to the nearest tenth?

  13. Example 6 The rectangular central chamber of the Lincoln Memorial is 74 ft long and 60 ft wide. Make a scale drawing of the floor of the chamber using a scale of 1 in.:20 ft.

  14. Example 7: Using Ratios to Find Perimeters and Areas Given that ∆LMN:∆QRT, find the perimeter P and area A of ∆QRS.

  15. Example 8 ∆ABC ~ ∆DEF, BC = 4 mm, and EF = 12 mm. If P = 42 mm and A = 96 mm2 for ∆DEF, find the perimeter and area of ∆ABC.

  16. Lesson Quiz: Part I 1. Maria is 4 ft 2 in. tall. To find the height of a flagpole, she measured her shadow and the pole’s shadow. What is the height h of the flagpole? 2. A blueprint for Latisha’s bedroom uses a scale of 1 in.:4 ft. Her bedroom on the blueprint is 3 in. long. How long is the actual room? 25 ft 12 ft

  17. Lesson Quiz: Part II 3. ∆ABC ~ ∆DEF. Find the perimeter and area of ∆ABC. P = 27 in., A = 31.5 in2

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