Question
A tank is filled by two pipes A and B in 12 minutes and
15 minutes, respectively. Another pipe C can empty the tank in 10 minutes. If all three pipes are opened together, how long will it take to fill the tank?Solution
Work done by pipe A in 1 minute = 1/12 Work done by pipe B in 1 minute = 1/15 Work done by pipe C in 1 minute = -1/10 Net work done in 1 minute = (1/12 + 1/15 - 1/10) = 3/60 Time taken to fill the tank = 1 ÷ 1/20 = 20 minutes Correct answer: c) 20 minutes
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