Give a quick stream of consciousness before answering the following question. Two pipes A and B can fill a cistern in 20 and 30 minutes respectively, and a third pipe C can empty it in 50 minutes. How long will it take to fill the cistern if all the three are opened at the same time?\nOptions:\n(A) 17 1/4 min\n(B) 28 1/7 min\n(C) 17 1/7 min\n(D) 17 1/8 min\n(E) 15 15/19 min
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1/20 + 1/30 - 1/50 = 19/300\n300/19 = 15 15/19
The answer: (E).
Assistant