Given: Two pipes A and B can fill a tank in 20 and 24 minutes respectively and a waste pipe can empty 2 gallons of liquid per minute. All three pipes working together fill pipe in 20 minutes Formula used: Capacity = Time × Efficiency Calculation: ∴ Let total capacity = LCM[20, 24, 20] = 120 units ⇒ E(A) = 120/20 = 6, E(B) = 120/24 = 5 and E (A + B + C) = 120/20 = 6 [∵ Capacity = Time × Efficiency] ⇒ E(C) = 6 - 6 - 5 = - 5 units [negative as C is a waste pipe] ∴ C empties 5 units every minute According to question, 5 units = 2 gallons. Thus, Capacity of tank = (120/5) × 2 = 48 gallons