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Published byNancy Warner Modified over 8 years ago

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Solving Proportions

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2 ways to solve proportions 1. Equivalent fractions (Old) Cross Products (New)

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Cross Products When you have a proportion (two equal ratios), then you have equivalent cross products. Find the cross product by multiplying the denominator of each ratio by the numerator of the other ratio.

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Example: Do the ratios form a proportion? Check using cross products. 4 12, 3 9 12 x 3 = 36 9 x 4 = 36 These two ratios DO form a proportion because their cross products are the same.

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Example 2 5 8, 2 3 8 x 2 = 16 3 x 5 = 15 No, these two ratios DO NOT form a proportion, because their cross products are different.

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Solving a Proportion Using Cross Products Use the cross products to create an equation. Solve the equation for the variable using the inverse operation.

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Example: Solve the Proportion 1. 19 38 = n 22 38n = 19(22) 38n = 418 38 n = 11

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Example: Solve the Proportion k 17 = 20 68 Start with the variable. = 68k17(20) Simplify. 68k=340 Now we have an equation. To get the k by itself, divide both sides by 68. 68 k = 5

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