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Math Help - problem with fractions and proportions

  1. #1
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    Post problem with fractions and proportions

    hi

    i have a mixture which has 87% of x and 13 % of y , which cannot be seperated.

    if i need to make a mixture with 99.5 % of x and 0.5 % of y, how much of x and y should i mix.

    pls answer quickly.
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  2. #2
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    Hello arch

    Welcome to Math Help Forum!
    Quote Originally Posted by arch View Post
    hi

    i have a mixture which has 87% of x and 13 % of y , which cannot be seperated.

    if i need to make a mixture with 99.5 % of x and 0.5 % of y, how much of x and y should i mix.

    pls answer quickly.
    You don't give us any quantity of the original mixture, but let me assume that there's 1 litre, and show you how to do that. Then you can work out how to do it for any other volume.

    In 1 litre of the mixture, 13%, or 0.13 litre, is y. We want to add a quantity of x so that this 0.13 litre is 0.5% of the new total volume. If we add v litres of x, the new total volume is (1+v) litres, and 0.5% of this is \frac{0.5}{100}(1+v). So we have:

     \frac{0.5}{100}(1+v) = 0.13

    \Rightarrow 0.5(1+v) = 13

    \Rightarrow 1 + v = 26

    \Rightarrow v = 25

    So for every litre of the original mixture, we must add 25 litres of x, in order to make the new mixture 99.5% x, 0.5% y.

    Grandad
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