Pipe A can fill a tank in 5 hours, Pipe B in 10 hours and Pipe C can empty it in 7.5 hours. If all three are opened together, the tank will be filled in:
Answer: A
Rate of Pipe A = 1/5 tank/hour. Rate of Pipe B = 1/10 tank/hour. Rate of Pipe C (emptying) = -1/7.5 = -2/15 tank/hour. When all are open, the combined rate = \(1/5 + 1/10 - 2/15\). The LCM of 5, 10, 15 is 30. Combined rate = \(\frac{6+3-4}{30} = \frac{5}{30} = \frac{1}{6}\) tank/hour. So, the tank will be filled in 6 hours.