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Math Help - Finding Value of X division of fractions

  1. #1
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    Finding Value of X division of fractions

    I am trying to help my son out and I am drawing a blank on this problem.

    x 7/8 = 3/5

    I know I have to do something like this:
    X x 8/7 = 3/5

    I am having problems with the solutions because of the reduced 3/5. Others we could eye ball and find the solution, but this one I am having difficulty with. Regards.
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  2. #2
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by zerbe View Post
    I am trying to help my son out and I am drawing a blank on this problem.

    x 7/8 = 3/5

    I know I have to do something like this:
    X x 8/7 = 3/5

    I am having problems with the solutions because of the reduced 3/5. Others we could eye ball and find the solution, but this one I am having difficulty with. Regards.
    now there are many ways to do this problem, a lot of room for creativity. but lets keep it simple.

    we want to get x by itself. why waste time making the left hand side pretty. just get rid of the 7/8 right off the bat

    x \div \frac 78 = \frac 35 .............multiply both sides by \frac 78 (do you see that this will cancel the 7/8 ?)

    we get

    x = \frac 35 \times \frac 78 ..............simplify

    \Rightarrow x = \frac {3(7)}{5(8)} = \frac {21}{40}
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  3. #3
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    Thanks so much. I have a tendency to make these problems more difficult than they are.
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  4. #4
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by zerbe View Post
    Thanks so much. I have a tendency to make these problems more difficult than they are.
    yes, the objective is to get x on one side by itself, and move everything to the other side. we move things by performing their opposite operation on both sides of the equation. so i wanted to move the 7/8 from the left. i noticed it was dividing, so i had to multiply both sides by 7/8. that way, the division cancels the multiplication on the left and i get rid of the 7/8 while at the same time, it ends up on the right, which is where i wanted to move it to
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  5. #5
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    There are two ways to do this, the guy above gave one, this is the other way:

    your right with your 8/7, multiplying by this is the same as dividing by 7/8.

    Thus you have x*8/7 = 3/5, this the same as 8x/7 = 3/5

    so then we multiply both sides by 7 to get rid of it form the 8x

    We do 3*7 which is 21

    so we have 8x = 21/5

    then simply divide both sides by 8, to get x = 21/5*8 which is 21/40.

    I hope this helped, if you need any more help just PM me.
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