Two pipes can fill a tank in 12 min and 15 min respectively. A third pipe empties it in 6 min. If all three operate, how long to empty a full tank?
A20 min
B30 min
C40 min
D60 min
Explanation
Net emptying rate = 1/6 – (1/12 + 1/15) = 1/6 – (5+4)/60 = 10/60 – 9/60 = 1/60 per min. Time to empty full tank = 60 minutes.
Exam Relevance
- Topic: Work and Time
- Subtopic: Pipes and Cisterns
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