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Unit 5 – Rates, Ratios, and Proportions Lesson 4 – Proportions and Scale Blue Handout Blue – Proportions and Scale 1. The scale on a map is 1/8 inch = 260 miles. How far apart are two cities that are 1 1 inches apart on the map? 16 2. The scale on a globe is 1/8 inch equals 125 miles. How many inches is the circumference of that globe? (Use 25,000 miles for the circumference of the earth.) Solutions 1. 2210 miles 1 1 1 inch 16 8 = Set up a proportion: 260 miles n miles Cross-multiply: 1 n= inch 17 •260 8 16 Divide both sides by 1/8 (which is the same as multiplying by 8/1): n = 2210 miles 2. 25 inches 1 inch ( globe ) n ( globe circumference ) 8 Set up a proportion: = 125 miles (real ) 25, 000 miles (real circumference ) Cross-multiply: 125n = 3125 Divide both sides by 125: n = 25 inches 1 Unit 5 – Rates, Ratios, and Proportions Lesson 4 – Proportions and Scale Blue Handout Bibliography Information Teachers attempted to cite the sources for the problems included in this problem set. In some cases, sources may not have been known. Problems Bibliography Information 1-2 Zaccaro, Edward. Challenge Math (Second Edition): Hickory Grove Press, 2005. 2