Two pipes can fill a tank in 20 and 24 min, respectively and a waste pipe can empty 6 gallon per min. All the three pipes working together can fill the tank in 15 min. Find the capacity of the tank.


A) 210 gallon

B) 50 gallon

C) 150 gallon

D) 240 gallon

Correct Answer:
D) 240 gallon

Description for Correct answer:
Part filled by 1st pipe = \( \Large \frac{1}{20} \)

Part filled by 2nd pipe in 1 min = \( \Large \frac{1}{24} \)

Part filled by all the pipes in 1 min = \( \Large \frac{1}{15} \)

Work done by the waste pipe in 1 min

= \( \Large \frac{1}{15}- \left(\frac{1}{20}+\frac{1}{24}\right)=\frac{1}{15}- \left(\frac{6+5}{120}\right) \)

= \( \Large \frac{1}{15}-\frac{11}{20} \)

= \( \Large \frac{8-11}{120}= \left(-\frac{3}{120}\right)= \left(-\frac{1}{40}\right) \) [-ve sign indicates emptying]

Now, volume of \( \frac{1}{40} \) part = 6 gallon

Therefore, Volume of whole tank = \( \Large 40 \times 6 \) = 240 gallon

Part of solved Pipes and Cisterns questions and answers : >> Aptitude >> Pipes and Cisterns








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