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Pipe & cistern
Q. A tank can be filled by two pipes A and B in 12 hours and 15 hours respectively. If both the pipes are opened together, how long will it take to fill the tank?
A) 6 hours
B) 7 hours
C) 8 hours
The part of the tank filled by pipe A in one hour is 1/12 and by pipe B in one hour is 1/15. So, the part of the tank filled by both the pipes in one hour is 1/12 + 1/15 = 9/60 = 3/20. Therefore, the time taken to fill the tank by both the pipes is 20/3 = 6.67 hours, which is approximately 8 hours.
D) 9 hours
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