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Homework Help: Speed distance velocity

  1. Jun 18, 2007 #1
    1. The problem statement, all variables and given/known data

    A plane flew 4200 km from Glasgow to Halifax into a head wind. With a tail wind, the plain flew 100km/h faster on the return trip. The total flying time from Glasgow to Halifax and back was 13 h. What was teh flying speed from glasgoq to Halifax?

    3. The attempt at a solution

    Speed x Time = Distance

    G-H x 4200/x 4200

    H-G x+100 4200/(x+100) 4200

    TOT 13h

    4200/x + 4200/(x+100) = 13 x (x)(x+100)

    4200(x+100) + 4200 (x) = (13)(x)(x+100) .....

    I kept doing this but none of these type of problems turn out right with me.
  2. jcsd
  3. Jun 18, 2007 #2


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    Homework Helper

    Looks good so far. It's just a quadratic equation. Keep going.
  4. Jun 18, 2007 #3


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    Homework Helper

    Oh, at first, looking at your post, it seems like a mess, and I have to quote it for easier reading. If you want to post things that needs "columns", and "rows", you can use the CODE tag, it's the sharp sign (i.e, #), it'll be much clearer. Like this:

    3. The attempt at a solution

    Code (Text):
                 Speed    x   Time     =     Distance

    G-H         x             4200/x           4200

    H-G         x+100      4200/(x+100)        4200

    TOT                         13h
    See? :)

    Back to your problem, the reddened line is wrong. It should have read:

    4200/x + 4200/(x+100) = 13

    Then, we multiply both sides by x(x + 100) to obtain your last line:

    4200(x + 100) + 4200x = 13 x(x + 100)

    Now, just expand everything out, isolate them to one side, and it's just a quadratic equation. :)
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