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Published byMiles Clark Modified over 8 years ago

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Proportions

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

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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.

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

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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

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

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

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

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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?

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

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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

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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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