Two pipes can fill a tank in 20 and 24 minutes respectively and a waste pipe can empty 3 gallons per minute. All the three pipes working together can fill the tank in 15 minutes. The capacity of the tank is:

Question: Two pipes can fill a tank in 20 and 24 minutes respectively and a waste pipe can empty 3 gallons per minute. All the three pipes working together can fill the tank in 15 minutes. The capacity of the tank is:Solution:Work done by the waste pipe in 1 minute= (1/15) - {(1/20 + 1/24 )}= (1/15) - (11/120)= - 1/40 [-ve sign means emptying]∴ Volume of 1/40 part = 3 gallons∴ Volume of whole = (3 × 40 ) gallons = 120 gallons