Pipes A and B can fill a tank in 8 hours and 12 hours respectively, and pipe C can empty the full tank in 24 hours. If all three pipes are opened together on an empty tank, how long will it take to fill?

💡 Solution & Explanation

Take the tank as 24 units (the LCM of 8, 12 and 24). Per hour, A fills 3 units, B fills 2 units and C empties 1 unit. Net filling = 3 + 2 − 1 = 4 units per hour. Time = 24 ÷ 4 = 6 hours. Adding C as a filling pipe would give 4 hours, which is too fast.