1.  Pipes A and B can fill a tank in 5 and 6 hours respectively. Pipe C can empty it in 12 hours. If all the three pipes are opened together, then the tank will be filled in:
A. 1(13/17) hours
B. 2(8/11) hours
C. 3(9/17) hours
D. 4(1/2) hours

Answer: Option C

Explanation:

Net part filled in 1 hour 1 + 1 - 1 = 17 .
5 6 12 60

The tank will be full in 60 hours i.e., 3 9 hours.
17 17