Quantitative Aptitude • Time, Speed & WorkHard
Pipes A and B can fill a tank in 20 hours and 30 hours respectively, and pipe C can empty the full tank in 60 hours. If all three pipes are opened together on an empty tank, how long will it take to fill?
A. 10 hours
B. 12 hours
C. 15 hours✓ Correct Answer
D. 60 hours
💡 Solution & Explanation
Take the tank as 60 units (the LCM of 20, 30 and 60). 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 = 60 ÷ 4 = 15 hours. Adding C as a filling pipe would give 10 hours, which is too fast.
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