Machine-translated by Google. Questions are authored in English.
Top

Pipes & Cistern Questions and Answers

Important Instructions
111.

To fill a cistern, pipes A, B and C take 20 minutes, 15 minute and 12 minutes respectively. The time in minutes that the three pipes together will take to fill the cistern is:

Answer: A

A can do a piece of work in x minutes
B can do a piece of work in y minutes
C can do a piece of work in z minutes
Minute’s work of each of the three is 1/x +1/y + 1/z
1 minutes work of each of the three pipes = 1/20 + 1/15 + 1/12
= 1/5 or = 5 minutes

Please log in or register to report this question.

Discuss in Forum
112.

Pipes A and B can fill a tank in 5 hours and 6 hours respectively. Pipe C can empty it in 12 hours. If all the three pipes are opened together, then the tank will be filled in.

Answer: B

Work in rates: a pipe that fills a tank in \( n \) units of time fills \( \tfrac{1}{n} \) of it per unit, and rates add (an emptying pipe counting negative).

\[ \frac{1}{5} + \frac{1}{6} - \frac{1}{12} \]

Over the common denominator 60:

\[ \frac{12 + 10 - 5}{60} = \frac{17}{60} \text{ per hour} \]

\[ t = \frac{60}{17} = 3\tfrac{9}{17} \text{ hours} \]

The emptying pipe subtracts, so the tank still fills - but more slowly than the \( 2\tfrac{8}{11} \) hours A and B would manage alone.

Please log in or register to report this question.

Discuss in Forum
113.

Pipe R can empty a full tank in 30 hours. But two pipes P and Q can fill a tank in 15 hours and 10 hours respectively. Ram unknowingly opened all three taps. After 2 hours Shyam realized it and closed Pipe R. Due to this mistake how much time more would it take to fill the tank?

Answer: B

Work in rates: a pipe that fills a tank in \( n \) units of time fills \( \tfrac{1}{n} \) of it per unit, and rates add (an emptying pipe counting negative).

With all three open:

\[ \frac{1}{15} + \frac{1}{10} - \frac{1}{30} = \frac{2 + 3 - 1}{30} = \frac{2}{15} \text{ per hour} \]

\[ 2 \text{ hours} \rightarrow \frac{4}{15} \text{ filled} \]

After R is closed, P and Q fill at \( \tfrac{1}{15} + \tfrac{1}{10} = \tfrac{1}{6} \):

\[ \frac{11}{15} \div \frac{1}{6} = 4.4 \text{ hours} \]

\[ \text{total} = 2 + 4.4 = 6.4 \text{ h}, \qquad \text{without the mistake} = 6 \text{ h} \]

\[ \text{extra} = 0.4 \text{ h} = 24 \text{ minutes} \]

Please log in or register to report this question.

Discuss in Forum
Loading…

Topics

Other Subjects

Tags: Pipes & Cistern Questions and Answers || Pipes & Cistern MCQ Questions and Answers || Pipes & Cistern GK Questions and Answers || Pipes & Cistern GK MCQ Questions || Pipes & Cistern Multiple Choice Questions and Answers || Pipes & Cistern GK || GK on Pipes & Cistern || Quantitative Aptitude Questions and Answers || Quantitative Aptitude MCQ Questions and Answers || Quantitative Aptitude GK Questions and Answers || GK on Quantitative Aptitude

About Us

ExamsRepo

Copyright © 2026 ExamsRepo . All Rights Reserved . With