• A cistern can be filled up in 4 h by an inlet A. An outlet B can empty the cistern in 8 h. If both A and B are opened simultaneously, then after how much time the cistern get filled?

    A) 5 h

      B) 7 h

    C) 8 h

      D) 6 h

    Correct Answer:
    C) 8 h

    Description for Correct answer
    Part filled by A in 1 h = \( \Large \frac{1}{4} \)

    Part emptied by B in 1 h = \( \Large \frac{1}{8} \)

    Part filled by(A + B) in 1 h

    = \( \Large \frac{1}{4}+ \left(-\frac{1}{8}\right)=\frac{1}{4}-\frac{1}{8}=\frac{2-1}{8}=\frac{1}{8} \)

    Therefore, Required time to fill the cistern = 8 h

    Note \( \Large \frac{-1}{8} \) has been taken because it empties the tank.

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A). 40 h B). 30 h
C). 50 h D). 30 h
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2). A pipe can fill a tank in 10 h, while an another pipe can empty it in 6 h. Find the time taken to empty the tank, when both the pipes are opened up simultaneously.
A). 11 h B). 15 h
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3). Three taps are fitted in a cistern. The empty cistern is filled by the first and the second taps in 3 and 4 h, respectively. The full cistern is emptied by the third tap in 5 h. If all three taps are opened simultaneously, the empty cistern will be filled up in
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4). Pipe A can fill a tank in 30 min, while pipe B can fill the same tank in 10 min and pipe C can empty the full tank in 40 min. If all the pipes are opened together, how much time will be needed to make the tank full?
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5). Pipes A and B can fill a tank in 5 and 6 h, respectively. Pipe C can fill it in 30 h. If all the three pipes are opened together, then in how much time the tank will be filled up?
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A). 16 h B). 20 h
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