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Pre-Algebra Glencoe 9.1 A ratio is a comparison of two numbers or measures using division. A ratio can be written three ways: 3:5 3/5 3 to 5 BACK Ratios are often expressed as fractions in simplest or as a decimal. 5 1 or .25 20 4 BACK A ratio is the comparison of two numbers with the same units by division. A ratio may be written in three ways. 2 to 3 2:3 2 3 What ratios can we form from the tiles above? part 12 to 8 part part whole 12 20 whole part 20 12 BACK Create as many ratios as possible. Write each ratio three different ways. BACK Simplest Form • Write the ratio 50 to 300 in simplest form. 1 50 300 6 BACK Simplest Form • Write the ratio 60¢ per dozen in simplest form. 5 60 1 12 BACK Look over the ratios you have written. Is there another way that you can write those ratios? The ratio illustrated here is four filled cells to ten total cells. The ratio shown here is two filled cells to five total cells. What do you know about these two ratios? How can you prove your answer? BACK Unit Rate To find the Unit Rate, you would find the cost or amount for 1. Or the rate when the denominator is 1. “How much for just 1?” BACK Unit Rate If it costs $78 for 13 sandwiches, What is the unit rate? $78 13 $6 each BACK The cost of a 12-ounce box of Cheerios is $3.29. Publix brand Cheerios cost $4.89 for an 18-ounce box. Find the unit rate to find the better buy. 3.29 4.89 .274 .271 12 18 BACK Mile per Gallon • M.P.G. stands for miles per gallon and is usually used for gas mileage in cars. BACK Unit Rate • If it takes 11 gallons to drive 250 miles, What is the unit rate or m.p.g.? BACK Solving Word Problems 250 x •Write problem as proportions: 11 1 •Solve using cross multiplication. 250(1) 11X 250 11X 11 11 BACK Now you try it! BACK