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Math Help - WordProblem with percentages

  1. #1
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    WordProblem with percentages

    If the water level of a pool dropped by 20% over night, by how much percent does it need to increase to get to the same level? Answer is 25%
    I set it up like this x-x80/100=y
    y+y(z/100)=x i dont know how to quantify a percentage differently and thats where i think I'm wrong..scratch that i know I'm wrong cause i have 2 equations with 3 variables. Can i get a hint? Don't want the full set up, i want to get it, cause ill feel stupid if i dont.
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  2. #2
    Member rtblue's Avatar
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    Try this equation (letting x be the original level of the water and y be the amount by which you increase the reduced level to get the original level):

    \displaystyle (.8x)(y)=x

    \displaystyle y=\frac{x}{.8x}

    The x's cancel out, and we have y=1/.8=5/4=1.25

    When we multiply by 1.25, we are increasing the value by 25%.
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