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Math Help - Percentage of a solution problem

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    Question Percentage of a solution problem

    In a certain medical test designed to measure carbohydrate tolerance, an adult drinks 7ounces of a a30% glucose solution. When thes test is administered to a child the glucose concentration must be decreased to 20%. How much 30% glucose solution and how much water should be used to prepare 7ounces of 20% glucose solution?
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  2. #2
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    Quote Originally Posted by amyl View Post
    In a certain medical test designed to measure carbohydrate tolerance, an adult drinks 7ounces of a a30% glucose solution. When thes test is administered to a child the glucose concentration must be decreased to 20%. How much 30% glucose solution and how much water should be used to prepare 7ounces of 20% glucose solution?
    If the solution is 20% glucose then it's 80% water.

    Let the amount of 30% glucose solution used be x ounces. Note that this solution is 70% water.

    Then the amount of pure water used is (7 - x) ounces and it's obviously 100% water.

    You want the result to be 80% water. So solve:

    (70/100)x + (100/100)(7 - x) = (80/100)(7), that is,

    0.7x + (7 - x) = (0.8)(7).
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