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Homework Help: Average Rate Problem

  1. Dec 7, 2009 #1
    1. The problem statement, all variables and given/known data

    Support you wish to average 40 mph on a trip and find that when you are half the distance to your distance to your destination you have averaged 30 mph. How fast should you travel in the remaining half of the trip to attain an overall average of 40 mph?

    2. Relevant equations

    d = rt

    3. The attempt at a solution

    I used S(avg) = x / (t1 + t2) = 40 mi/hr

    I substituted (2d/60) for t1 and (d/2r) for t2.

    Doing some algebraic manipulations, I got r = 60 mph. Is this correct?
  2. jcsd
  3. Dec 8, 2009 #2


    Staff: Mentor

    Yes, and this is easy enough to check.
  4. Dec 8, 2009 #3
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