 # Proportions. Proportion – two equal ratios 1 = 4 3 = 15 2 8 5 25 7 = 21 a = c 8 24 b d.

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Proportions

Proportion – two equal ratios 1 = 4 3 = 15 2 8 5 25 7 = 21 a = c 8 24 b d

Do the ratios form a proportion? 3 9 In a proportion, the 7 21 cross products are equal. 3 21 = 63 Yes, the ratios 7 9 = 63 form a proportion.

Do the ratios form a proportion? 2 8 Yes 10 40 9 12 No 12 15

Solving Proportions: You can solve for a missing value in a proportion. 1) cross multiply to form an equation 2) solve the equation to find the missing value

Examples: x = 9 12x = 36 4 12 x = 3 y = 18 45y = 90 5 45 y = 2

Solve these proportions: 8 = 20 n 30 20n = 240 n = 12

5 = 35 8 x 5x = 280 x = 56

You can use a proportion to solve an everyday problem. If you can buy three posters for \$9.60, how many can you buy for \$48.00?

3 posters = x posters \$ 9.60 \$48.00 \$ 9.60x = \$ 144.00 x = 15

At the Copy Shop, 18 copies cost \$1.08. How much will 40 copies cost? 18 copies = 40 copies \$1.08 \$ y 18y = \$43.20 y = \$ 2.40

If you can drive 100 miles in 4 hours, how many miles can you drive in 10 hours? 100 miles = x miles 4 hours 10 hours 4x = 1000 x = 250 miles

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