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?
Select the correct option:  A) 820 gallons  B) 128 gallons  C) 120 gallons  D) 129 gallons  E) 220 gallons
Work done by the waste pipe in 1 minute = 1/15 - (1/20 + 1/24) = - 1/40   Volume of 1/40 part = 3 gallons\   Volume of whole = 3 * 40= 
<gadget id="calculator">3 * 40</gadget>
<output>120</output>
120 gallons.   Answer: 120 gallons
<result>C</result>
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?