# Pipes and Cisterns

- The problems of pipes and cisterns usually have two kinds of pipes, Inlet pipe and Outlet pipe / Leak. Inlet pipe is the pipe that fills the tank/reservoir/cistern and Outlet pipe / Leak is the one that empties it.
- If a pipe can fill a tank in ‘n’ hours, then in 1 hour, it will fill ‘1 / n’ parts. For example, if a pipe takes 6 hours to fill a tank completely, say of 12 liters, then in 1 hour, it will fill 1 / 6 th of the tank, i.e., 2 liters … More on Pipes and Cisterns

Question 1 |

7 minutes | |

7 minutes 30 seconds | |

6 minutes | |

6 minutes 3 seconds |

**Explanation:**

Question 2 |

Two pipes X and Y attached to a swimming pool can fill the pool in 20 minutes and 30 minutes respectively working alone. Both were opened together but due to malfunctioning of motor of pipe X, it had to be shut down after two minutes but Y continued to work till the swimming pool was filled completely. Find the total time taken to fill the pool.

27 | |

22 | |

25 | |

20 |

**Explanation:**

Let the capacity of the pool be LCM(20, 30) = 60 units. => Efficiency of pipe X = 60 / 20 = 3 units / minute => Efficiency of pipe Y = 60 / 30 = 2 units / minute => Combined efficiency of pipe X and pipe Y = 5 units / minute Now, the pool is filled with the efficiency of 5 units / minute for two minutes. => Pool filled in two minutes = 10 units => Pool still empty = 60 - 10 = 50 units This 50 units is filled by Y alone. => Time required to fill these 50 units = 50 / 2 = 25 minutes Therefore, total time required to fill the pool = 2 + 25 = 27 minutes

Question 3 |

6 minutes | |

6 minutes 15 seconds | |

6 minutes 40 seconds | |

6 minutes 50 seconds |

**Explanation:**

Question 4 |

1 | |

1.5 | |

2 | |

3 |

**Explanation:**

Question 5 |

6 | |

6.5 | |

7 | |

7.5 |

**Explanation:**

^{2}= a x b, where 'a' and 'b' are the extra time taken if both work individually than if both work together. Therefore, n

^{2}= 9 x 6.25 => n = 3 x 2.5 = 7.5 Thus, working together, pipes A and B require 7.5 hours.

Question 6 |

5 | |

6 | |

7 | |

8 |

**Explanation:**

Question 7 |

12 : 00 PM | |

12 : 30 PM | |

1 : 30 PM | |

1 : 00 PM |

**Explanation:**

Question 8 |

20 hours | |

25 hours | |

30 hours | |

35 hours |

**Explanation:**

Question 9 |

7 hours 14 minutes | |

6 hours 54 minutes | |

5 hours 14 minutes | |

8 hours 54 minutes |

**Explanation:**

Question 10 |

600 | |

400 | |

800 | |

700 |

**Explanation:**