Student: 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?\nOptions:\n(A) 299\n(B) 2767\n(C) 120\n(D) 287\n(E) 261.
Another student: Let's say, hmmm...

User
Work done by the waste pipe in 1 minute = 1/15 - (1/20 + 1/24) = - 1/40\nVolume of 1/40 part = 3 gallons\\nVolume of whole = 3 * 40 = 120 gallons. Final answer: (C).
Assistant