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Homework Help: Can anyone help with an average speed problem?

  1. Sep 25, 2011 #1
    1. The problem statement, all variables and given/known data

    A racing team of 3 drivers drove a 24 hour event in shifts. The first driver drove only one fourth of the race but averaged 140km/hr. The second driver drove one third of the race at an average speed of 170 km/hr. The last driver drove the remainder of the race at 160 km/hr. What was the average speed of the team?

    2. Relevant equations
    I do not know how to set up the problem in order to find average speed since there is no specific distance


    3. The attempt at a solution
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Sep 25, 2011 #2
    Well, this is kind of an odd question. I would think that a weighted average could work. E.g. multiply the first speed by 1/4, the second by 1/3, and the third by 5/12. Then add these numbers together. See if that gives you the right answer, I'm not entirely sure.
     
  4. Sep 25, 2011 #3
    You have the total time: T=24h
    Then, t1=[itex]\frac{1}{4}[/itex]T=6h
    t2=[itex]\frac{1}{3}[/itex]T=8h
    t3=[itex]\frac{5}{12}[/itex]T=10h

    The distance of each shift:
    d1=v1*t1
    d2=v2*t2
    d3=v3*t3

    Now you have the total distance and the total time, so you can calculate the average speed.
     
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