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.
A) 60 gallons B) 80 gallons C) 120 gallons D) 160 gallons E) None
Solution   Work done by the waste pipe in 1 minute   =1/15-(1/20+1/24)   = (1/15-11/20)   = - 1/40	[ - ve sigh means emptying]   Volume of 1/40 part	= 3 gallons.   Volume of Whole	= (3×40)   =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