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Homework Help: Physics convert units

  1. Jan 19, 2012 #1
    1. The problem statement, all variables and given/known data

    A large school district has 300 school buses. If each school bus is used 3 hours each day, the average speed of the school buses is 15 mi/h, and the fuel economy of the buses is 10 mi/gal. How much does it cost to run these buses in 22 school days if gasoline costs $1.20 a gallon?

    2. The attempt at a solution

    I've been trying to figure out this problem for hours now. This is what I've done, but the book says I'm incorrect.

    My attempt:

    Find out what it costs to run one bus a day.

    3 hrs/day x 15 mi/hr x 1gal/10mi x $1.20/gal = $5.40 per day for 1 bus.

    There are 300 buses, so $5.40 x 300 = $1620 for 300 buses.

    The problem asks the cost for running the buses for 22 school days, $1620 * 22 = $35,640.

    My final answer is that it would cost $35,640 to run 300 buses for 22 days. Please help me figure out where I am going wrong.
     
  2. jcsd
  3. Jan 19, 2012 #2

    phyzguy

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    Science Advisor

    Your analysis looks good to me. What does the book say is the right answer?
     
  4. Jan 19, 2012 #3
    Thanks for the quick response. The answer seems to be $216.
     
  5. Jan 19, 2012 #4

    phyzguy

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    Science Advisor

    I think that $216 can't possibly be the right answer to the problem you posed. Are you sure you copied it correctly?
     
  6. Jan 19, 2012 #5
    I'll double check when I get home tonight. I appreciate your help!
     
  7. Jan 19, 2012 #6
    Sorry for the late response. Book has the answer as $1200.
     
  8. Jan 20, 2012 #7

    Delphi51

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    Homework Helper

    Your $35640 matches my calc exactly!
     
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