Pipes A, B and C can fill a tank in 20, 30 and 60 hours, respectively. Pipes A, B and C are opened at 7 a.m., 8 a.m. and 9 a.m. respectively, on the same day. When will the tank be full?
Show answer & explanation
Correct answer: B
Explanation
The correct answer is option 2 i.e. 5:40 p.m.
Pipes A, B and C can fill a tank in 20, 30 and 60 hours.
Let the total work will be LCM of (20, 30, 60) = 60 units.
Efficiency of A = 60/20 = 3 units/ hour.
Efficiency of B = 60/30 = 2 units/ hour
Efficiency of C = 60/60 = 1 units/hour.
Work done by A till 9 am = 3 × 2 = 6 units
Work done by B till 9 am = 2 units.
Total work done till 9am = 6 + 2 = 8 units
Remaining work = 60 - 8 = 52.
Time taken by all the pipes to fill the tank = 52/6 = 8 hours and 40 minutes.
9 am + 8 hours 40 minutes = 5 : 40 pm.