Understanding Proportion Example:

What is a ratio? Write a ratio for the following in as many ways as you can: Boys to girls Boys to students Girls to students How would these change if we got a new female student?

Ratio A ratio is the comparison of two numbers by division. A classroom has 16 boys and 12 girls. Also written as16 boys, 16:12 or 16 to girls Generally, ratios are in lowest terms: 16 = 16/4 = /4 3

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

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

Ratio, continued If a ratio is part-to-whole, you can divide and find a decimal or a percent. 16 boys 31 students 16/31 =.516, or 51.6% are boys

Let’s Practice! SB p. 81 #9-10 with shoulder partner (6 min) Should partners compare with face

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

Proportion, continued Tires cost two for $75. How much will four tires cost? # 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 One more way to solve proportions: Cross Products 2 = 6 2 x n = 6 x 8 2n = 48 8 n 2 2 n = 24

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

Let’s Practice SB p.84 #6-8 with face partner

Exit Slip Write and solve a proportion for the following: If Marcie pays $4.80 for three pounds of strawberries, how much will she pay for seven pounds?