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Pipes & Cisterns Questions with Solutions

6 questions4 easy2 medium

Pipes and cisterns questions are an application of time and work. An inlet pipe fills a tank and does positive work, while an outlet pipe or leak empties it and does negative work. If an inlet pipe fills a tank in a hours, it fills 1/a of the tank each hour. If an outlet pipe empties it in b hours, it removes 1/b each hour. Questions involve several pipes opened together, pipes opened or closed partway through, leaks that slow down filling, and pipes with different filling rates. The LCM method works especially well. Take the tank's capacity as the LCM of the given times, find each pipe's rate in units per hour (negative for outlet pipes and leaks), and add the rates. This avoids fractions entirely. Always check whether the question asks for the time to fill or the time to empty. Practise the pipes and cisterns questions below, each with a step-by-step solution using the LCM method.

All QuestionsEasyMediumHard
  1. Q1.

    Pipe A can fill a tank in 12 hours and pipe B can fill it in 15 hours. If both pipes are opened together, the tank will be filled in

    A. 6 h 20 minB. 6 h 40 minC. 7 hD. 7 h 30 min
    easyView solution ›
  2. Q2.

    A pipe can fill a tank in 10 hours and an outlet pipe can empty the full tank in 15 hours. If both are opened together on an empty tank, the tank will be full in

    A. 6 hB. 25 hC. 30 hD. 12.5 h
    easyView solution ›
  3. Q3.

    Pipes A and B can fill a tank in 20 minutes and 30 minutes respectively. Both are opened together, and after 6 minutes pipe A is closed. How much more time will B take to fill the tank?

    A. 12 minB. 15 minC. 18 minD. 21 min
    mediumView solution ›
  4. Q4.

    Three pipes A, B and C can fill a tank in 6 hours, 8 hours and 12 hours respectively. If all three are opened together, the tank will be filled in

    A. 2 h 40 minB. 2 h 30 minC. 3 hD. 3 h 20 min
    easyView solution ›
  5. Q5.

    A pipe can fill a tank in 8 hours. Because of a leak at the bottom, it takes 10 hours to fill the tank. In how many hours can the leak alone empty the full tank?

    A. 18B. 20C. 40D. 80
    mediumView solution ›
  6. Q6.

    Two pipes A and B can fill the cistern in 37.5 minutes and 45 minutes respectively. Both pipes are opened. The cistern will be filled in just half an hour, if the B is turned off after

    A. 5 minutesB. 9 minutesC. 10 minutesD. 15 minutes
    easyAsked in NIMCET 2020 +1View solution ›