Two pipes can fill a tank in 12 minutes and 15 minutes respectively. A third pipe can empty it in 20 minutes. How long will it take to fill the tank if all three are open?
A8 minutes
B10 minutes
C12 minutes
D15 minutes
Explanation
Net filling rate per minute = 1/12 + 1/15 – 1/20 = (5 + 4 – 3) / 60 = 6 / 60 = 1/10. Time required = 10 minutes.
Exam Relevance
- Topic: Work and Time
- Subtopic: Pipes and Cisterns
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