Understanding Proportion Ratio l A ratio is the

Understanding Proportion

Ratio l A ratio is the comparison of two numbers by division. l A classroom has 16 boys and 12 girls. Also written as 16 boys�, 16: 12 or 16 to 12 12 girls l Generally, ratios are in lowest terms: 16 = 16/4 = 4 12 12/4 3 l

Ratio, continued l Ratios can compare two unlike things: Joe earned $40 in five hours l The ratio is 40 dollars or 8 dollars 5 hours 1 hour l l When the denominator is one, this is called a unit rate.

Ratio, continued Let’s look at a classroom: l Ratios can be part-to-part l 16 boys 15 girls l Ratios l can be part-to-whole 16 boys 31 students

Ratio, continued l If a ratio is part-to-whole, you can divide and find a decimal or a percent. l 16 boys 31 students 31/16. 00 =. 516, or 51. 6% are boys

Proportion l Proportion is a statement that says two ratios are equal. l In an election, Damon got three votes for each two votes that Shannon got. Damon got 72 votes. How many votes did Shannon get? l Damon 3 = 72 so 3 x 24 = 72 Shannon 2 x 24 48 n = 48, so Shannon got 48 votes.

Proportion, continued l Tires cost two for $75. How much will four tires cost? l # of tires 2 = 4 so 2 x 2 = 4 tires cost 75 n 75 x 2 $150 n = 150, so four tires cost $150

Proportion, continued l One l 2 more way to solve proportions: =6 8 n 2 xn=6 x 8 n = 24 2 n = 48 2 2

Proportion, continued l Now you try! l Three cans of soup costs $5. How much will 12 cans cost? l# of cans 3 = 12 3 x 4 = 12 cans cost 5 n 5 x 4 20 dollars n = 20, so 12 cans cost $20