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Thread: Fillit up

  1. #1
    Member pHaTaL_eRrOr's Avatar
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    Fillit up

    A large water tank has two inlet pipes (a large one and a small one) and one outlet pipe. It takes 2 hours to fill the tank with the large inlet pipe. On the other hand, it takes 5 hours to fill the tank with the small inlet pipe. The outlet pipe allows the full tank to be emptied in 7 hours.

    What fraction of the tank (initially empty) will be filled in 0.45 hours if all three pipes are in operation? Give your answer to two decimal places (e.g., 0.25, 0.5, or 0.75).

  2. #2
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    .25

  3. #3
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    My Work
    Large Inlet Pipe
    1 tank = 2 hours
    (1/2 tank = 1 hour) * .45
    .225 tank = .45 hour)
    Small Inlet Pipe
    1 tank = 5 hours
    (1/5 tank = 1 hour) * .45
    .09 tank = .45 hour)
    Outlet Pipe
    1 tank = 7 hours
    (1/7 tank = 1 hour) * .45
    .064... tank = .45 hour)
    .225 + .09 - .064 = .25

  4. #4
    Member -=DoW=- Lago's Avatar
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    A small fact that you forgot to mention. where is the location of the outlet pipe? If it's located at the bottom of the tank then it will release water from the time it starts filling compared to if the outlet was placed in the middle or top of the tank.
    Have i read too much into this yet
    The killing was the best part. It was the dying I couldn't take.
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  5. #5
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    I assumed it was on the bottom of the tank.

  6. #6
    the large inlet pipe fills 1 / 3 of the tank;
    the small inlet pipe fills 1 / 4 of the tank;
    the outlet pipe empties 1 / 7 of the tank; and therefore
    all three pipes together fill [ (1 / 3) + (1 / 4) - (1 / 7) ] of the tank.

    Fraction of the tank that will be filled in 2.3 hours =

    2.3 [ (1 / 3) + (1 / 4) - (1 / 7) ] = 1.

  7. #7
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    ^ What this dude said.

  8. #8
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    Actually, I agree with Lago.
    The Outlet pipe could be attached vertically to the top, in which case the tank would not empty unless it were to overflow or be compressed.

  9. #9

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    re: Fillit up

    0.45 * (1/2+1/5-1/7)=0.2507143

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