Pipes and Cistern


  1. Three pipes A, B and C can fill a tank separately in 8 h,10 h and 20h, respectively. Find the time taken by all the three pipes to fill the tank when these pipes are opened together ?









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    Part filled by A in 1 h = 1/8
    Part filled by B in 1 h = 1/10
    Part filled by C in 1 h = 1/20
    Part filled by (A + B + C) in 1 h = 1/8 + 1/10 + 1/20

    Correct Option: D

    Part filled by A in 1 h = 1/8
    Part filled by B in 1 h = 1/10
    Part filled by C in 1 h = 1/20
    Part filled by (A + B + C) in 1 h = 1/8 + 1/10 + 1/20
    = (5 + 4 + 2)/40 = 11/40
    ∴ Required time to fill the tank = 40/11 h
    = 37/11 h


  1. A tap can fill a tank in 16 minutes and another can empty it in 8 minutes. If the tank is already half full and both the taps are opened together, the tank will be ?









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    Part emptied in 1 min. = (1/8 - 1/16) = 1/16
    ∴ Time taken to empty the full tank = 16 min.

    Correct Option: D

    Part emptied in 1 min. = (1/8 - 1/16) = 1/16
    ∴ Time taken to empty the full tank = 16 min.
    Hence, time taken to empty the half tank = 8 min.



  1. A cistern can be filled by two pipes A and B in 4 hours and 6 hours respectively. When full, the tank can be emptied by a third pipe C in 8 hours . If all the taps be turned on at the same time, the cistern will be full in ?









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    Net filling in 1 hour = (1/4 + 1/6 - 1/8) = 7/24

    Correct Option: B

    Net filling in 1 hour = (1/4 + 1/6 - 1/8) = 7/24
    ∴ Time taken to fill the cistern = (24/7) hrs. = 3 hrs. 26 min.


  1. One tap can fill a cistern in 2 hours and another can empty the cistern in 3 hours. How long will they take to fill the cistern if both the taps are opened ?









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    Net filling in 1 hour = (1/2 - 1/3) = 1/6

    Correct Option: B

    Net filling in 1 hour = (1/2 - 1/3) = 1/6
    ∴ Time taken to fill the cistern = 6 hours



  1. A pipe can fill a tank in x hours and another can empty it in y hours. They can together fill it in (y > x) ?









  1. View Hint View Answer Discuss in Forum

    Net filling in 1 hour = (1/x - 1/y) = (y - x) / xy

    Correct Option: D

    Net filling in 1 hour = (1/x - 1/y) = (y - x) / xy
    ∴ Time taken to fill the tank = xy / (y - x) hrs.