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Geometry Ratio: Date: ____ §12.4 Proportions Comparison of 2 quantities of the same unit. 2 ratios (or rates) set equal. Proportion: Means-Extremes Property: If a c = , then ad = bc. (cross multiply) b d extremes means Examples: 1. ∆DEF is the image of ∆ABC under a size change with center O. If AB = 20, DE = 12, and DF = 16.5 find AC. 2. A toy train is 48 actual size. If the locomotive of the train is 10 8 inches long and 24 inches high, how long and how high is the actual locomotive? 1 7 1 3. A Boeing 747 is about 70.5 meters long and has a wingspan of about 59.6 meters. The wingspan on a model of this plane is 40 centimeters. What will be the length of the model? 4. One law of physics states that the amount of pressure that a gas exerts is proportional to the temperature of the gas in Kelvins (K), assuming a constant volume. If a gas exerts 16 lbs/in2 of pressure at a temperature of 298 K, how much pressure would the gas exert at 278 K? pressure temperature