Two pipes A and B can separately fill a tank in 20 and 15 minutes respectively. A third pipe C can drain off 45 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?
Options.
A) 590 liters	B) 540 liters	C) 820 liters	D) 900 liters	E) 580 liters
1/20 + 1/15 - 1/x   = 1/15   x = 12   20 * 45= 
<gadget id="calculator">20 * 45</gadget>
<output>900</output>
900   Answer:900 liters
<result>D</result>
Two pipes A and B can separately fill a tank in 20 and 15 minutes respectively. A third pipe C can drain off 45 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?