Pipes and Cisterns is an important topic in mathematics and quantitative aptitude. It is commonly asked in SSC, banking, railway, state government exams, entrance tests and campus placements. The topic is useful because it checks both concept and calculation speed.
This lesson explains pipes and cisterns in simple language with formulas, shortcut tricks, solved examples, practice questions and FAQs. The goal is to make the topic easy for beginners and useful for exam revision.
What Is Pipes and Cisterns?
Pipes and cisterns questions are time and work problems where pipes fill or empty a tank. Filling pipes do positive work and emptying pipes do negative work.
Important Terms
| Point | Details |
|---|---|
| Inlet | Pipe that fills a tank |
| Outlet | Pipe that empties a tank |
| Leak | Opening that removes water |
| Tank capacity | Total work, usually taken as 1 or LCM units |
| Net rate | Filling rate minus emptying rate |
Important Formulas
| Point | Details |
|---|---|
| Pipe fills in x hours | One hour work = 1/x |
| Pipe empties in y hours | One hour work = -1/y |
| Two inlets | Add both filling rates |
| Inlet and outlet | Subtract outlet rate from inlet rate |
| Time | Total tank / net rate |
Step-by-Step Method
- Find one-hour work of each pipe.
- Mark inlet as positive and outlet as negative.
- Add or subtract rates to get net rate.
- Find time by dividing tank capacity by net rate.
- If tank is partly filled, use only remaining part.
Shortcut Tricks
- Use LCM of times as tank capacity.
- Inlet adds water, outlet removes water.
- If outlet rate is higher, tank empties.
- For partly filled tank, calculate remaining work.
- Convert minutes into hours when needed.
Common Question Types
| Point | Details |
|---|---|
| Single inlet | Tank filling |
| Single outlet | Tank emptying |
| Two inlets | Combined filling |
| Inlet and leak | Net filling |
| Partly filled tank | Remaining work |
Solved Examples
Example 1
A pipe fills a tank in 10 hours. What part is filled in 1 hour?
1/10 of the tank.
Example 2
A pipe empties a tank in 15 hours. What part is emptied in 1 hour?
1/15 of the tank.
Example 3
Pipes A and B fill a tank in 6 and 12 hours. Find time together.
1/6 + 1/12 = 1/4. Time = 4 hours.
Example 4
An inlet fills in 8 hours and leak empties in 24 hours. Find net filling time.
1/8 – 1/24 = 1/12. Time = 12 hours.
Example 5
A pipe fills half tank in 5 hours. Time for full tank?
Full tank takes 10 hours.
Exam Style Examples
Question 1
A fills a tank in 5 hours and B empties it in 10 hours. If both are open, find time to fill.
Net rate = 1/5 – 1/10 = 1/10. Time = 10 hours.
Outlet is subtracted.
Question 2
Two pipes fill in 12 and 18 hours. How much tank is filled in 3 hours?
Together rate = 1/12 + 1/18 = 5/36. In 3 hours = 15/36 = 5/12.
Question asks part filled, not total time.
Question 3
A tank is 1/3 full. A pipe fills remaining tank in 8 hours. Find time for full tank by that pipe.
Remaining = 2/3. If 2/3 takes 8 hours, full takes 8 x 3/2 = 12 hours.
Use remaining part carefully.
Common Mistakes
- Not subtracting outlet work.
- Adding time values directly.
- Ignoring partly filled tank.
- Using minutes and hours together.
- Writing negative net filling as final filling time.
Practice Questions
- Pipe fills in 20 hours. One hour work?
- Pipe empties in 30 hours. One hour emptying?
- Pipes fill in 10 and 15 hours. Time together?
- Inlet fills in 6 hours, leak empties in 12 hours. Net time?
- Two pipes fill in 8 and 24 hours. Time together?
- A pipe fills 1/4 tank in 3 hours. Full time?
- Tank is half full. Pipe fills full tank in 10 hours. Remaining time?
- Pipe A fills in 12 hours, B empties in 18 hours. Net filling time?
- A and B together fill in 5 hours. A alone fills in 10 hours. B alone?
- Three pipes fill in 6, 8, 12 hours. Time together?
Answers to Practice Questions
- 1/20
- 1/30
- 6 hours
- 12 hours
- 6 hours
- 12 hours
- 5 hours
- 36 hours
- 10 hours
- 2 hours 40 minutes
Frequently Asked Questions
What is an inlet?
An inlet is a pipe that fills a tank.
What is an outlet?
An outlet is a pipe that empties a tank.
How are pipes and cisterns related to time and work?
The tank is treated as total work and each pipe has a work rate.
What is net rate?
Net rate is filling rate minus emptying rate.
Which method is fastest?
The LCM method is usually fastest for exam questions.
Revision Notes
Pipes and cisterns are time and work questions. Add filling rates and subtract emptying rates.
Revise the main formula and then solve at least five direct questions. After that, solve mixed word problems. This order gives better clarity and speed.
Conclusion
Pipes and cisterns are easy when each pipe is converted into one-hour work.
Additional Exam Practice Note
In Pipes and Cisterns, most questions follow fixed patterns. Read the condition carefully and convert it into a formula. If two actions happen together, combine their rates or cases properly. If the question asks for probability, count favourable and total outcomes. If the question asks for tank filling or emptying, treat filling as positive and emptying as negative.
Students should practise easy questions first and then move to mixed examples. Timed practice is helpful only after the concept is clear. Accuracy should come before speed.
Before final answer, check whether the value is possible. A probability must be between 0 and 1. A tank filling time must be positive. Such checks reduce mistakes in exams.
Additional Exam Practice Note
In Pipes and Cisterns, most questions follow fixed patterns. Read the condition carefully and convert it into a formula. If two actions happen together, combine their rates or cases properly. If the question asks for probability, count favourable and total outcomes. If the question asks for tank filling or emptying, treat filling as positive and emptying as negative.
Students should practise easy questions first and then move to mixed examples. Timed practice is helpful only after the concept is clear. Accuracy should come before speed.
Before final answer, check whether the value is possible. A probability must be between 0 and 1. A tank filling time must be positive. Such checks reduce mistakes in exams.
Additional Exam Practice Note
In Pipes and Cisterns, most questions follow fixed patterns. Read the condition carefully and convert it into a formula. If two actions happen together, combine their rates or cases properly. If the question asks for probability, count favourable and total outcomes. If the question asks for tank filling or emptying, treat filling as positive and emptying as negative.
Students should practise easy questions first and then move to mixed examples. Timed practice is helpful only after the concept is clear. Accuracy should come before speed.
Before final answer, check whether the value is possible. A probability must be between 0 and 1. A tank filling time must be positive. Such checks reduce mistakes in exams.
Additional Exam Practice Note
In Pipes and Cisterns, most questions follow fixed patterns. Read the condition carefully and convert it into a formula. If two actions happen together, combine their rates or cases properly. If the question asks for probability, count favourable and total outcomes. If the question asks for tank filling or emptying, treat filling as positive and emptying as negative.
Students should practise easy questions first and then move to mixed examples. Timed practice is helpful only after the concept is clear. Accuracy should come before speed.
Before final answer, check whether the value is possible. A probability must be between 0 and 1. A tank filling time must be positive. Such checks reduce mistakes in exams.
Additional Exam Practice Note
In Pipes and Cisterns, most questions follow fixed patterns. Read the condition carefully and convert it into a formula. If two actions happen together, combine their rates or cases properly. If the question asks for probability, count favourable and total outcomes. If the question asks for tank filling or emptying, treat filling as positive and emptying as negative.
Students should practise easy questions first and then move to mixed examples. Timed practice is helpful only after the concept is clear. Accuracy should come before speed.
Before final answer, check whether the value is possible. A probability must be between 0 and 1. A tank filling time must be positive. Such checks reduce mistakes in exams.
Additional Exam Practice Note
In Pipes and Cisterns, most questions follow fixed patterns. Read the condition carefully and convert it into a formula. If two actions happen together, combine their rates or cases properly. If the question asks for probability, count favourable and total outcomes. If the question asks for tank filling or emptying, treat filling as positive and emptying as negative.
Students should practise easy questions first and then move to mixed examples. Timed practice is helpful only after the concept is clear. Accuracy should come before speed.
Before final answer, check whether the value is possible. A probability must be between 0 and 1. A tank filling time must be positive. Such checks reduce mistakes in exams.
Additional Exam Practice Note
In Pipes and Cisterns, most questions follow fixed patterns. Read the condition carefully and convert it into a formula. If two actions happen together, combine their rates or cases properly. If the question asks for probability, count favourable and total outcomes. If the question asks for tank filling or emptying, treat filling as positive and emptying as negative.
Students should practise easy questions first and then move to mixed examples. Timed practice is helpful only after the concept is clear. Accuracy should come before speed.
Before final answer, check whether the value is possible. A probability must be between 0 and 1. A tank filling time must be positive. Such checks reduce mistakes in exams.
Additional Exam Practice Note
In Pipes and Cisterns, most questions follow fixed patterns. Read the condition carefully and convert it into a formula. If two actions happen together, combine their rates or cases properly. If the question asks for probability, count favourable and total outcomes. If the question asks for tank filling or emptying, treat filling as positive and emptying as negative.
Students should practise easy questions first and then move to mixed examples. Timed practice is helpful only after the concept is clear. Accuracy should come before speed.
Before final answer, check whether the value is possible. A probability must be between 0 and 1. A tank filling time must be positive. Such checks reduce mistakes in exams.
Additional Exam Practice Note
In Pipes and Cisterns, most questions follow fixed patterns. Read the condition carefully and convert it into a formula. If two actions happen together, combine their rates or cases properly. If the question asks for probability, count favourable and total outcomes. If the question asks for tank filling or emptying, treat filling as positive and emptying as negative.
Students should practise easy questions first and then move to mixed examples. Timed practice is helpful only after the concept is clear. Accuracy should come before speed.
Before final answer, check whether the value is possible. A probability must be between 0 and 1. A tank filling time must be positive. Such checks reduce mistakes in exams.
Additional Exam Practice Note
In Pipes and Cisterns, most questions follow fixed patterns. Read the condition carefully and convert it into a formula. If two actions happen together, combine their rates or cases properly. If the question asks for probability, count favourable and total outcomes. If the question asks for tank filling or emptying, treat filling as positive and emptying as negative.
Students should practise easy questions first and then move to mixed examples. Timed practice is helpful only after the concept is clear. Accuracy should come before speed.
Before final answer, check whether the value is possible. A probability must be between 0 and 1. A tank filling time must be positive. Such checks reduce mistakes in exams.
Additional Exam Practice Note
In Pipes and Cisterns, most questions follow fixed patterns. Read the condition carefully and convert it into a formula. If two actions happen together, combine their rates or cases properly. If the question asks for probability, count favourable and total outcomes. If the question asks for tank filling or emptying, treat filling as positive and emptying as negative.
Students should practise easy questions first and then move to mixed examples. Timed practice is helpful only after the concept is clear. Accuracy should come before speed.
Before final answer, check whether the value is possible. A probability must be between 0 and 1. A tank filling time must be positive. Such checks reduce mistakes in exams.
Additional Exam Practice Note
In Pipes and Cisterns, most questions follow fixed patterns. Read the condition carefully and convert it into a formula. If two actions happen together, combine their rates or cases properly. If the question asks for probability, count favourable and total outcomes. If the question asks for tank filling or emptying, treat filling as positive and emptying as negative.
Students should practise easy questions first and then move to mixed examples. Timed practice is helpful only after the concept is clear. Accuracy should come before speed.
Before final answer, check whether the value is possible. A probability must be between 0 and 1. A tank filling time must be positive. Such checks reduce mistakes in exams.
Additional Exam Practice Note
In Pipes and Cisterns, most questions follow fixed patterns. Read the condition carefully and convert it into a formula. If two actions happen together, combine their rates or cases properly. If the question asks for probability, count favourable and total outcomes. If the question asks for tank filling or emptying, treat filling as positive and emptying as negative.
Students should practise easy questions first and then move to mixed examples. Timed practice is helpful only after the concept is clear. Accuracy should come before speed.
Before final answer, check whether the value is possible. A probability must be between 0 and 1. A tank filling time must be positive. Such checks reduce mistakes in exams.
Additional Exam Practice Note
In Pipes and Cisterns, most questions follow fixed patterns. Read the condition carefully and convert it into a formula. If two actions happen together, combine their rates or cases properly. If the question asks for probability, count favourable and total outcomes. If the question asks for tank filling or emptying, treat filling as positive and emptying as negative.
Students should practise easy questions first and then move to mixed examples. Timed practice is helpful only after the concept is clear. Accuracy should come before speed.
Before final answer, check whether the value is possible. A probability must be between 0 and 1. A tank filling time must be positive. Such checks reduce mistakes in exams.
Additional Exam Practice Note
In Pipes and Cisterns, most questions follow fixed patterns. Read the condition carefully and convert it into a formula. If two actions happen together, combine their rates or cases properly. If the question asks for probability, count favourable and total outcomes. If the question asks for tank filling or emptying, treat filling as positive and emptying as negative.
Students should practise easy questions first and then move to mixed examples. Timed practice is helpful only after the concept is clear. Accuracy should come before speed.
Before final answer, check whether the value is possible. A probability must be between 0 and 1. A tank filling time must be positive. Such checks reduce mistakes in exams.
Additional Exam Practice Note
In Pipes and Cisterns, most questions follow fixed patterns. Read the condition carefully and convert it into a formula. If two actions happen together, combine their rates or cases properly. If the question asks for probability, count favourable and total outcomes. If the question asks for tank filling or emptying, treat filling as positive and emptying as negative.
Students should practise easy questions first and then move to mixed examples. Timed practice is helpful only after the concept is clear. Accuracy should come before speed.
Before final answer, check whether the value is possible. A probability must be between 0 and 1. A tank filling time must be positive. Such checks reduce mistakes in exams.
Additional Exam Practice Note
In Pipes and Cisterns, most questions follow fixed patterns. Read the condition carefully and convert it into a formula. If two actions happen together, combine their rates or cases properly. If the question asks for probability, count favourable and total outcomes. If the question asks for tank filling or emptying, treat filling as positive and emptying as negative.
Students should practise easy questions first and then move to mixed examples. Timed practice is helpful only after the concept is clear. Accuracy should come before speed.
Before final answer, check whether the value is possible. A probability must be between 0 and 1. A tank filling time must be positive. Such checks reduce mistakes in exams.
Additional Exam Practice Note
In Pipes and Cisterns, most questions follow fixed patterns. Read the condition carefully and convert it into a formula. If two actions happen together, combine their rates or cases properly. If the question asks for probability, count favourable and total outcomes. If the question asks for tank filling or emptying, treat filling as positive and emptying as negative.
Students should practise easy questions first and then move to mixed examples. Timed practice is helpful only after the concept is clear. Accuracy should come before speed.
Before final answer, check whether the value is possible. A probability must be between 0 and 1. A tank filling time must be positive. Such checks reduce mistakes in exams.
Additional Exam Practice Note
In Pipes and Cisterns, most questions follow fixed patterns. Read the condition carefully and convert it into a formula. If two actions happen together, combine their rates or cases properly. If the question asks for probability, count favourable and total outcomes. If the question asks for tank filling or emptying, treat filling as positive and emptying as negative.
Students should practise easy questions first and then move to mixed examples. Timed practice is helpful only after the concept is clear. Accuracy should come before speed.
Before final answer, check whether the value is possible. A probability must be between 0 and 1. A tank filling time must be positive. Such checks reduce mistakes in exams.