Question
Two pipes, A and B, can fill a tank in 12 hours and 15
hours respectively, while a third pipe, C, can empty the tank in 10 hours. If all three pipes are opened simultaneously, in how many hours will the tank be full?Solution
Work done by A in 1 hour = 1/12, Work done by B in 1 hour = 1/15 Work done by C in 1 hour (emptying) = -1/10 Net work done in 1 hour = (1/12) + (1/15) - (1/10) Taking LCM of 12, 15, and 10 = 60, Net work = (5/60) + (4/60) - (6/60) = 3/60 = 1/20 The tank will be filled in 20 hours. Correct Option: a) 20 hours
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