Subject: mathqa
Question: two pipes a and b can separately fill a tank in 10 and 15 minutes respectively . a third pipe c can drain off 20 liters of water per minute . if all the pipes are opened , the tank can be filled in 15 minutes . what is the capacity of the tank ?
Option: 
A: 540 liters
B: 560 liters
C: 580 liters
D: 200 liters
Answer: D