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Math Help - Word Problems

  1. #1
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    Word Problems

    If one outlet pipe can drain a tank in 24 hours and another pipe can drain the tank in 36 hours, how long will it take for both pipes to drain the tank?

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  2. #2
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    Re: Word Problems

    One way to look at this is to imagine both pipes connected to 2 identical tanks.
    Consider the pipes to have started draining tanks at the same time.
    In 36 hours, pipe B will drain one tank.
    In the first 24 hours, pipe A will have drained the other tank
    and would be able to drain another half tank in the last 12 hours.
    Hence, the taps operating simultaneously could drain 2.5 tanks in 36 hours.
    How long will it take to drain one tank ?

    Yet another way is...
    in 12 hours, one pipe will have drained half the tank
    while the other pipe will have drained a third.
    That's 3 sixths and 2 sixths.
    In 12 hours, 5 sixths will be drained.
    How much longer for another sixth ?
    Last edited by Archie Meade; July 10th 2011 at 03:47 PM. Reason: added alternative
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  3. #3
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    Re: Word Problems

    Quote Originally Posted by theloser View Post
    If one outlet pipe can drain a tank in 24 hours and another pipe can drain the tank in 36 hours, how long will it take for both pipes to drain the tank?

    Have no clue how to set this up? Help Thanks
    setting up these "job type" problems ...

    (combined rates to do the job)(time for job completion) = 1 job completed

    \left(\frac{1 \, tank}{24 \, hrs} + \frac{1 \, tank}{36 \, hrs}\right) \cdot (t \, hrs) = 1 \, tank \, drained

    solve for
    t \, hrs
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