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Published byAimee Ingersoll Modified over 2 years ago

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Alligation/Alternate Purpose: An easy method to make a new strength from two existing strengths

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Sample Problem Triamcinolone cream is available in strengths of 0.1% and 0.5%. What quantity of 0.1% and 0.5% cream is needed to make 100 grams of 0.2% triamcinolone cream?

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Basic Set Up % strength starting Material #1 % strength starting Material #2 % strength desired (final product) % strength starting material #1 minus % strength desired (absolute value) % strength starting material #2 minus % strength desired (absolute value) 0.1 0.5 0.2 0.3 0.1

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% strength starting material #2 minus % strength desired (absolute value) % strength starting material #1 minus % strength desired (absolute value) Value is the # of parts needed of starting material #1 Value is the # of parts needed of starting material #2 Total # of parts needed 0.3 0.1 0.3 0.4

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Value is the # of parts needed of starting material #2 Value is the # of parts needed of starting material #1 Total # of parts needed Ratio needed for starting material #1 Ratio needed for starting material #2 0.3 0.1 0.4 0.75 0.25

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Ratio needed for starting material #1 Ratio needed for starting material #2 Final amount of product desired Amount needed of starting material #1 Amount needed of starting material #2 0.75 0.25 100 grams 75 grams 0.1% cream 25 grams 0.5% cream

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Answer 75 grams 0.1% cream 25 grams 0.5% cream 100 grams 0.2% cream

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Example Problem How much of a 20% hydrocortisone (HC) cream and how much of a 5% HC cream would be needed to make 50 grams of a 9% HC cream?

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Basic Set Up 20% 5% 9% 11 parts 4 parts

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11 parts 4 parts 11 parts 15 parts

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11 parts 4 parts15 parts 0.267 0.733

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50 grams 13.3 grams 36.7 grams 0.267 0.733 50 grams

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36.7 grams of 5% HC cream 13.3 grams of 20% HC cream 50 grams of 9% HC cream

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Created by: Jeff Sundell & Doug White

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