Solution: Just open the C tube, and the empty pool can be filled in 60 hours. It can be known that the working efficiency of C pipe is 1/60.

By opening pipes A and C at the same time, the whole pool can be emptied within 20 hours. It can be known that the efficiency of tube A minus the efficiency of tube C is equal to 1/20, so the efficiency of tube A is:

1/20+ 1/60= 1/ 15,

Similarly, the working efficiency of the second pipeline is:1/30+1/60 =1/20.

So, at the same time open a, b, c three pipeline work efficiency and is:

1/ 15+ 1/20- 1/60= 1/ 10

The time to drain a pool of water is:

1÷110 =10 hour.