Two pumps are connected to an empty tank. Pump X fills the tank with water at a constant rate, while pump Y drains water out of the tank at a constant rate. The two pumps finish filling the tank in two times the duration it would take pump X alone to fill the tank. If pump Y alone can empty a whole tank in 30 minutes, then how many minutes does it take pump X alone to fill the tank?
Options
A) 15	B) 16	C) 18	D) 20	E) 24
Let V be the volume of the tank.   Let R be the rate per minute that pump X fills the tank.   Let T be the time it takes pump X to fill the tank.   The rate at which pump Y empties the tank is V/30 per minute.   (R - V/30)*2T=V=RT.   (R-V/30)*2=R   R=V/15.   It takes pump X 15 minutes to fill the tank.   The answer is 15.
<result>A</result>
Two pumps are connected to an empty tank. Pump X fills the tank with water at a constant rate, while pump Y drains water out of the tank at a constant rate. The two pumps finish filling the tank in two times the duration it would take pump X alone to fill the tank. If pump Y alone can empty a whole tank in 30 minutes, then how many minutes does it take pump X alone to fill the tank?