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Understanding Proportion

Understanding Proportion. Example:. What is a ratio?. Write a ratio for the following in as many ways as you can: B oys 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.

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Understanding Proportion

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  1. Understanding Proportion Example:

  2. 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?

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

  4. 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.

  5. Ratio, continued Let’s look at a classroom again: • Ratios can be part-to-part • 16 boys15 girls • Ratios can be part-to-whole • 16 boys31 students

  6. Ratio, continued • If a ratio is part-to-whole, you can divide and find a decimal or a percent. • 16 boys31 students 16/31 = .516, or 51.6%are boys

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

  8. 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 24 48 n = 48, so Shannon got 48 votes.

  9. Proportion, continued • Tires cost two for $75. How much will four tires cost? • # of tires2 = 4 so 2 x 2 = 4 tires cost 75 n 75 x 2 $150 n = 150, so four tires cost $150

  10. Proportion, continued • One more way to solve proportions: Cross Products 2 = 62 x n = 6 x 82n = 48 8 n 2 2 n = 24

  11. Proportion, continued • Now you try! • Three cans of soup costs $5. How much will 12 cans cost? • # of cans3 = 123 x 4 = 12 cans cost 5 n 5 x 4 20 dollars n = 20, so 12 cans cost $20

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

  13. 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?

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