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A cistern is provided with two pipes A and B. A can fill it in 20 minutes and B can empty it in 30 minutes. If A and B be kept open alternately for one minute each, how soon will the cistern be filled ?
  • a)
    120 minutes
  • b)
    121 minutes
  • c)
    110 minutes
  • d)
    115 minutes
Correct answer is option 'D'. Can you explain this answer?
Most Upvoted Answer
A cistern is provided with two pipes A and B. A can fill it in 20 minu...


Given Data:
- Pipe A fills the cistern in 20 minutes.
- Pipe B empties the cistern in 30 minutes.

Approach:
- Let's calculate the efficiency of each pipe.
- Efficiency = 1/Time taken by the pipe to fill or empty the cistern.

Calculations:
- Efficiency of pipe A = 1/20
- Efficiency of pipe B = -1/30 (negative because it empties the cistern)

Time taken to fill the cistern using both pipes:
- Combined efficiency = Efficiency of A - Efficiency of B
- Combined efficiency = 1/20 - 1/30 = 1/60

- Time taken to fill the cistern with both pipes open alternately for 1 minute each = 2 minutes (1 minute each for A and B)

Final Calculation:
- Time taken to fill the cistern with both pipes open alternately for 2 minutes each = 60/1 x 2 = 120 minutes

Therefore, the cistern will be filled in 120 minutes if pipes A and B are kept open alternately for 1 minute each. Hence, option a) 120 minutes is correct.
Free Test
Community Answer
A cistern is provided with two pipes A and B. A can fill it in 20 minu...
Using Rule 7,
Part of the tank filled in first two minutes

Part of tank filled in 114 minutes
= 57/60 = 19/20
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A cistern is provided with two pipes A and B. A can fill it in 20 minutes and B can empty it in 30 minutes. If A and B be kept open alternately for one minute each, how soon will the cistern be filled ?a)120 minutesb)121 minutesc)110 minutesd)115 minutesCorrect answer is option 'D'. Can you explain this answer?
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A cistern is provided with two pipes A and B. A can fill it in 20 minutes and B can empty it in 30 minutes. If A and B be kept open alternately for one minute each, how soon will the cistern be filled ?a)120 minutesb)121 minutesc)110 minutesd)115 minutesCorrect answer is option 'D'. Can you explain this answer? for SSC CGL 2024 is part of SSC CGL preparation. The Question and answers have been prepared according to the SSC CGL exam syllabus. Information about A cistern is provided with two pipes A and B. A can fill it in 20 minutes and B can empty it in 30 minutes. If A and B be kept open alternately for one minute each, how soon will the cistern be filled ?a)120 minutesb)121 minutesc)110 minutesd)115 minutesCorrect answer is option 'D'. Can you explain this answer? covers all topics & solutions for SSC CGL 2024 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for A cistern is provided with two pipes A and B. A can fill it in 20 minutes and B can empty it in 30 minutes. If A and B be kept open alternately for one minute each, how soon will the cistern be filled ?a)120 minutesb)121 minutesc)110 minutesd)115 minutesCorrect answer is option 'D'. Can you explain this answer?.
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