Q. Pipes A, B and C are attached to an empty cistern. While the first two can fill the cistern in 4 and 10 hrs, respectively, the third can drain the cistern, when filled, in 6 hrs. If all the three pipes are opened simultaneously when the cistern is half-full, how many hours will be needed to fill the cistern?
A) 60/11
B) 30/11
C) 90/11
D) 120/11
✔ Correct Answer: 30/11
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