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Quadratic equations - problems

  1. May 26, 2015 #1
    • Missing template due to originally being posted in non-homework forum
    A train travels a distance of 480km at a uniform speed. If the speed had been 8km/h less, then it would have taken 3 hours more to cover the same distance. Find the speed of the train.
    Represent this situation in the form of quadratic equation.

    So I have been trying this but couldn't find it.
    I have taken the speed as x.
    And time, t
    Distance =speed *time
    I couldn't go any further. And I'm not sure if this is right or not.
    I just started learning quadratic equations. And I don't have any depth in the subject. Help me solve it in an easy way. Thank you!
  2. jcsd
  3. May 26, 2015 #2


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    Generally, avoid using x for speed as it is more regularly used for distances.

    Apart from that (and the fact your quantities are missing units), you are doing well. You have two equations and two unknowns. Solve for t in one of them (I suggest the first) and insert the result into the other.
  4. May 26, 2015 #3


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    I have no problem with using "x" for speed! And in problems like this distance is more often "s" or "d".
    (Though, personally, I would have used "v".)

    It would be better to say that t is the time required to travel 480 km at the original speed. Just "t is time" is ambiguous. And it would be better to say "x is the speed in km per hour and t is in hours" but those are a bit picky!

    From 480= xt,, t= 480/x. Replace t in the second equation with that to get a single equation in x.
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