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Two pipes A and B can fill a cistern in 12 minutes and 15 minutes respectively but a third pipe C can empty the full tank in 6 minutes. A and B are kept open for 5 minutes in the begining and then C is also opened. In what time will the cistern be emptied?
  • a)
    30 min
  • b)
    33 min
  • c)
    37.5 min
  • d)
    45 min
Correct answer is option 'D'. Can you explain this answer?
Verified Answer
Two pipes A and B can fill a cistern in 12 minutes and 15 minutes resp...
A and B are kept for 5 minutes i.e. 5 ( 1/12 + 1/15 ) = 3/4
When A, B and C pipes are opened = 1/12 + 1/15 - 1/6 = - 1/60
Empty the cistern in 1 min is 1/60
So 3 4 Will emptied in 3/4/1/60 = 45 minutes
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Most Upvoted Answer
Two pipes A and B can fill a cistern in 12 minutes and 15 minutes resp...
Given:
Pipe A fills the cistern in 12 minutes.
Pipe B fills the cistern in 15 minutes.
Pipe C empties the cistern in 6 minutes.
A and B are kept open for 5 minutes before C is opened.

To find:
Time taken to empty the cistern.

Solution:
Let the capacity of the cistern be 60 units (LCM of 12, 15, and 6).
Pipe A can fill 5 units of the cistern in 1 minute.
Pipe B can fill 4 units of the cistern in 1 minute.
Pipe C can empty 10 units of the cistern in 1 minute (60/6).

After 5 minutes, the cistern will have 25 units of water (5*5).
Let t be the time taken to empty the cistern.
During this time, A and B will fill (5t) units of water.
Pipe C will empty (10t) units of water.

Therefore, the total amount of water in the cistern after t minutes will be (25 + 5t - 10t) units.
We want this to be equal to the capacity of the cistern, which is 60 units.
25 - 5t = 60
-5t = 35
t = 7

Therefore, the cistern will be emptied in 5 + 7 = 12 minutes.

Answer: (D) 45 min.
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Two pipes A and B can fill a cistern in 12 minutes and 15 minutes respectively but a third pipe C can empty the full tank in 6 minutes. A and B are kept open for 5 minutes in the begining and then C is also opened. In what time will the cistern be emptied?a)30 minb)33 minc)37.5 mind)45 minCorrect answer is option 'D'. Can you explain this answer?
Question Description
Two pipes A and B can fill a cistern in 12 minutes and 15 minutes respectively but a third pipe C can empty the full tank in 6 minutes. A and B are kept open for 5 minutes in the begining and then C is also opened. In what time will the cistern be emptied?a)30 minb)33 minc)37.5 mind)45 minCorrect answer is option 'D'. Can you explain this answer? for Railways 2024 is part of Railways preparation. The Question and answers have been prepared according to the Railways exam syllabus. Information about Two pipes A and B can fill a cistern in 12 minutes and 15 minutes respectively but a third pipe C can empty the full tank in 6 minutes. A and B are kept open for 5 minutes in the begining and then C is also opened. In what time will the cistern be emptied?a)30 minb)33 minc)37.5 mind)45 minCorrect answer is option 'D'. Can you explain this answer? covers all topics & solutions for Railways 2024 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for Two pipes A and B can fill a cistern in 12 minutes and 15 minutes respectively but a third pipe C can empty the full tank in 6 minutes. A and B are kept open for 5 minutes in the begining and then C is also opened. In what time will the cistern be emptied?a)30 minb)33 minc)37.5 mind)45 minCorrect answer is option 'D'. Can you explain this answer?.
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