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9-3 6 th grade math Finding a Percent of a Number

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Objective To use a proportion to set up percent problems and solve using cross products. Why? To know find discounts and sales prices.

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California State Standards NS 1.4 : Calculate given percentages of quantities … AF 2.0: Use … rules to solve problems involving … proportions. MR 2.2: Apply strategies and results from simpler problems to more complex problems. MR 3.2: Note the method of deriving the solution and demonstrate a conceptual understanding of the derivation by solving problems.

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Percent Problems: 3 ways Find a part, given a percent and the whole – “What is 40% of 75?” X = 40% x 75 Find a percent, given the whole and a part – “What percent of 50 is 20?” X% x 50 = 20 Find a whole, given a percent and a part – “35% of what number is 70?” 35% x X = 70

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How to Find a Percent of a Number 1)Write equation, using the % symbol. a)‘of’ means x b)‘is’ means equals 2) Translate the equation: change the % to a decimal and solve. 3) Check answer for reasonableness How much money will you save if you buy jeans on sale that originally costs $60. Sale is 30% off. 60 x 30% = 60 x.30 = 18.00 You will save $18

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Writing a Proportion to Find a Percent of a Number How to write a proportion 1)Write the first ratio: The % will change into a fraction with 100 as the denominator 2)Write the second ratio: The $ amount will be the denominator and n will be the numerator. 3) Solve using cross products Find 40% of 75. 40 = n 100 75 100n = 3000 n = 3000 ÷ 100 n = 30

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Try It! 1)40% of 120 2)25% of 245 3)120% of 60 4)6% of 25 1).40 x 120 = 48 2).25 x 245 = 61.25 3) 1.20 x 60 =72 4).06 x 25 = 1.5

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Try Some More! 5) 10% of 46 6) 35% of 90 7) 45% of 50 8) 100% of 7 5).10 x 46 = 4.8 6).35 x 90 = 31.5 7).45 x 50 = 22.5 8) 1.00 x 7 = 7

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Objective Review To use a proportion to set up percent problems and solve using cross products. Why? You now know to find discounts and sales prices. Proportional reasoning can be used to set up problems involving finding a percent of a number. The proportion can be solved using cross-products.

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Independent Practice Complete problems 10- 17 Copy original problem first. Show all work! If time, complete Mixed Review: 18-27 If still more time, work on Accelerated Math.

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