Pipes and Cistern

By : Kanika Ralhan

Updated : Oct 7, 2020, 12:32

Pipes and Cistern is an important part of the Quantitative Aptitude section in Competitive Banking examinations and Government examinations like SBI PO, IBPS CLERK, SBI SO, IBPS RRB, IBPS PO, SBI CLERK, NABARD GRADE A & B, RBI GRADE A & B, and more.

In this section, you will need to answer questions about the rate at which we can fill a container using a pipe. The problems in this section will be similar to the ones in the Time & Work section. We’re going to provide you with Pipes and Cistern notes for bank exams, Pipes and Cistern online tests series questions and answers, quiz, syllabus for bank exams, notes for bank exams, and more.

A cistern is a container used for holding liquids. Cisterns are built for catching and preserving rainwater. Most modern cisterns range in capacity from a few litres to hundreds of cubic metres. Pipes are connected to these cisterns or containers. They are used to either fill or empty the cisterns and are of the following types:

• INLET: A Pipe that fills up the Cistern.
• OUTLET: A Pipe that empties the Cistern.

Important Pipes and Cistern Topics for Bank Exams

 TOPIC EXPLANATION RULE 1 If a pipe can fill a container in ‘x’ hours, then in 1 hour, it will fill (1/x) parts. RULE 2 If a pipe can empty a container in ‘y’ hours, then in 1 hour, it will empty (1/y) parts. INLET PIPE A pipe that fills up the cistern or container. OUTLET PIPE A pipe that empties the cistern or container. RULE 3 If both the Inlet and Outlet pipes are opened simultaneously, then the net part of the container filled in 1 hour will be (1/x-1/y). RULE 4 If 2 inlets, A and B, are opened simultaneously, then the net part of the tank filled in 1 hour will be (1/x+1/y).

Tricks & Tricks to Solve Pipes & Cistern Questions

• LCM METHOD: Let’s say there are 2 Pipes, A and B. A fills the container in 20 minutes and B empties the same in 60 minutes. Take the LCM of the given Numbers. Now this LCM will be the total capacity of the cistern. So the LCM = (20,60) = 60.
• Outlets may also be referred to as ‘Leak’ in the question. If Leak time > Inlet Pipe, then the container will get filled. However, if Leak Time < Inlet Pipe, then the container will get emptied.
• Net work done = (Sum of work done by inlets) - (Sum of work done by outlets)

Importance of Pipes & Cistern in Aptitude Section of Competetive Banking exams

• HIGH SCORING: Due to the similarity with the Time & Work section, Pipes & Cistern questions are fairly easy to solve.
• TIME-SAVING: If you use the tips mentioned above and practise well, you’re likely to answer the questions quickly and save time for the tougher sections.
• REPETITION OVER THE YEARS: Similar questions have been repeated over the years.

• FAMILIARITY: As you’ve studied this concept over the years, you’ll surely be familiar with the basic concepts.

Most Recommended Books for Pipes & Cistern

 QUANTITATIVE APTITUDE DR. R.S. AGGARWAL QUANTITATIVE APTITUDE ARUN SHARMA

Why Prepare Pipes & Cistern from BYJU'S Exam Prep?

Looking for a one-stop solution to prepare for Pipes and Cistern? Then choose BYJU'S Exam Prep. At BYJU'S Exam Prep, we believe that learning should be fun, not mundane. From our easy to learn videos, quizzes, and online mock test series, we provide our students with detailed solutions and quick hacks. We have an expert faculty who curate fresh questions, based on the latest exam pattern. You can expect Quizzes, notes, syllabus, problems and solutions, previous year papers, and tips and tricks amongst other things.

Pipes and Cistern is a fairly easy topic to master if your concepts are clear. If you’re aware of the basic terminologies and practise daily from the previous year question papers, in addition to our quizzes, notes and tricks, you’ll surely be able to solve all the questions in no time. Don’t forget to check out the books recommended by us and the entire syllabus on our portal.

QUESTION 1. X and Y can fill a cistern in 20 and 30 respectively, while Z can empty it in 40 minutes. If all three are opened at the same time, how long will it take to fill the cistern?

SOLUTION. 1/20 + 1/30 - 1/40 = 7/120

= 17 1/7

QUESTION 2. Pipe H can fill a container in 6 hours. After half of it is filled, three similar taps are opened. How long will it take to fill the tank completely?

SOLUTION. Time taken by H to fill half the tank = 3 hours.

Part filled by 4 taps in 1 hour = 4 x 1/16 = 2/3

Remaining part = 12

So 23:12: 1:X

So total time taken = 3 hours 45 minutes

QUESTION 3. C, D AND E are three pipes that can fill a tank in 6 hours. After 2 hours, C is closed. D and E can fill the remaining part in 7 hours. How long will C take to fill the tank alone?

SOLUTION. The part that gets filled in 2 hours = 2/6 = ⅓

(D + E)’s 7 hours of work = 2/3

So their 1 hour of work = 2/21

C’s one hour of work = {(D+E+C)’S one hour of work} - {(A+B)’s 1 hour of work}

= 1/6 - 2/21 = 1/14

C can fill the tank in 14 hours.

QUESTION 4. 2 Pipes fill a tank in 20 minutes and 24 minutes respectively while another tap empties 3 Gallons per minute. When all of them work together, they can fill the cistern in 15 minutes. Calculate the capacity of the tank.

SOLUTION. Work done by 3rd Pipe in 1 minute = -140 (-ve sign means emptying)

Value of 140part = 3 Gallons

Thus, Volume of whole = 3x40 = 120 Gallons

QUESTION 5. S and T fill up a tank in 10 and 15 minutes respectively. When the waste pipe is open, they do the same in 18 minutes. How long will it take for the waste pipe to empty the entire tank?

SOLUTION. So, 1/10 + 1/15 - 1/x = 1/18

X = 9

Thus, the waste pipe can empty the entire tank in 9 hours.

QUESTION 6. A container takes 3 1/2 hours to get filled by a Pipe. As there is a leak at the bottom, it’ll take half an hour extra to do the same. If the container is full, how long will it take to empty it?

SOLUTION. 2/7 - 1/X = 1/4

X = 28

Thus, it’ll take 28 hours to empty the container.

QUESTION 1. Will it help if I’ve studied the Time and Work concept before starting Pipes and Cistern?

SOLUTION. It’s definitely beneficial if you’ve already studied Time and Work. As the concepts are very similar, it’ll be easier for you to solve the problems.

QUESTION 2. How many questions are expected from this section?

SOLUTION. You can get up to 2-3 questions from this topic. However, there’s also a possibility that no question comes from this topic too. It’s always better to be prepared though.

QUESTION 3. A tank that usually gets filled in 8 hours, takes 2 hours longer due to a leak at the bottom. If the tank is full, how long will it take for the leak to empty it?

SOLUTION. 1/8 - 1/X = 1/10

So X = 40

Thus, it’ll take 40 hours for the leak to empty it.

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