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Pipes A and B can fill a tank in 20 h and 30 h, respectively and pipe C can empty the full tank in 40 h. If all the pipes are opened together, how much time will be needed to make the tank full ?
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- 161/7 h
- 171/7 h
- 181/7 h
- 191/7 h
Correct Option: B
Net part filed in 1 h = (1/20 + 1/30 - 1/40) = 7/120
Hence, the tank will be full in 120/7 = 171/7 h
