Pipes and Cisterns Cheat Sheet
31 Oct 2026
Quick answer
A quick revision cheat sheet on pipes and cisterns for SSC, Banking, Railway and state exams. It covers the rate idea, how to combine inlet pipes, how an outlet pipe subtracts, the time for pipes working together, and the net filling rate, with worked examples to revise quickly before the exam.
Pipes and Cisterns Cheat Sheet
Quick Revision
Pipes and cisterns is the same idea as time and work: a pipe that fills a tank in x hours does 1/x of the tank each hour. Inlet pipes add; outlet pipes subtract.
1. The Rate Idea
A pipe that fills a tank in x hours fills 1/x of it per hour.2. Pipes Working Together
For two inlet pipes filling in x and y hours:
Rate together = 1/x + 1/y
Time together = (x × y) / (x + y)3. An Outlet Pipe
An outlet (drain) pipe empties, so its rate is subtracted:
Net rate = 1/x + 1/y − 1/zIf the net rate is negative, the tank is being emptied overall.
4. Worked Example
Pipe A fills a tank in 6 hours, pipe B in 4 hours. Opened together:
Rate = 1/6 + 1/4 = 2/12 + 3/12 = 5/12 per hour
Time = 12/5 = 2.4 hours = 2 hours 24 minutes5. Exam Quick Tips
- Always convert "fills in
xhours" to the rate1/xbefore combining. - An outlet pipe's rate is negative — subtract it.
- The time for pipes together is the reciprocal of the combined rate.
Keep revising with the rest of the Maths section:
How this was made: Drafted with AI assistance; spot-checked by the editor on 31 October 2026.