Pipe A can fill a tank in 5 hours, pipe B in 10 hours and pipe C in 30 hours. If all the pipes are open, in how many hours will the tank be filled?\nOptions:\n(A) 2\n(B) 3\n(C) 3.5\n(D) 4\n(E) 4.5 Think first, then make a decision. Some random thoughts:
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Part filled by A + B + C in 1 hour = 1/5 + 1/10 + 1/30 = 1/3\nAll the three pipes together will fill the tank in 3 hours. So the answer is (B).
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