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Math Help - Need help with this word problem

  1. #1
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    Need help with this word problem

    John is concerned about body fat. He weighs 200 lbs and has 25% body fat.
    Body fat percentage can be found using the following formula.


    100 x Amount of body fat/total body weight = % body fat which would be
    100 x X/200=25%

    They ask to find the amount of body fat.

    I came up with this formula

    25/100 x 200 = X

    So X would be 50 lbs for the amount of body fat

    then they ask how much weight he would lose if he was down to 18% body fat

    18/100 x 200 = X

    so that would be 36 lbs

    Am i completely off? or do i have this correct?
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  2. #2
    Super Member Anonymous1's Avatar
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    Quote Originally Posted by bhigz View Post
    John is concerned about body fat. He weighs 200 lbs and has 25% body fat.
    Body fat percentage can be found using the following formula.


    100 x Amount of body fat/total body weight = % body fat which would be
    100 x X/200=25%

    They ask to find the amount of body fat.

    I came up with this formula

    25/100 x 200 = X

    So X would be 50 lbs for the amount of body fat

    then they ask how much weight he would lose if he was down to 18% body fat

    18/100 x 200 = X

    so that would be 36 lbs

    Am i completely off? or do i have this correct?
    You are right.

    100\cdot \frac{W}{200} = BFP \Rightarrow  \frac{W}{2} = BFP \Rightarrow W = 2\cdot BFP

    W_1 = 2\cdot (25) = \fbox{50}

    W_2 = 2\cdot (18) = 36

    So he lost W_1 - W_2 = 50 - 36 = \fbox{14}
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