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Thread: Distance formula confusion

  1. #1
    Sep 2016

    Question Distance formula confusion

    The question below states that at noon, Deirdre and Donovan were 1100 miles apart? According to the question, Deirdre boarded the train at 12pm and Donovan 2 hours later. Is there a typo in this book or am I missing something?

    Deirdre and Donovan are in love and will be meeting in Kansas City to get married.
    Deirdre boarded a train at noon traveling due east toward Kansas City. Two hours later, Donovan boarded a train traveling due west, also heading for Kansas City, and going at a rate of speed 20 miles per hour faster than Deirdre. At noon, they were, 1,100 miles apart. At 9 pm. they, they both arrived at Kansas City. How fast are they traveling?

    Distance of Deirdre from Kansas City + Distance of Donovan from Kansas City = 1,100
    Rate x Time + Rate x Time = 1,100

    Thanks in advance.
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  2. #2
    MHF Contributor
    Feb 2015
    Ottawa Ontario

    Re: Distance formula confusion

    Let a mph = Deirdre's speed;
    so Donovan's speed = a+20 mph

    time by Deirdre = 9 hours; so:
    distance by Deirdre = 9a;
    so distance by Donovan = 1100 - 9a

    time by Donovan = 7 hours; so:
    distance by Donovan also = 7(a + 20); so:
    1100 - 9a = 7(a + 20)

    Solve for a
    Last edited by DenisB; Jun 9th 2017 at 06:51 PM.
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