Pipes A and B can fill a tank in 20 hours and 30 hours respectively while pipe C can empty the full tank in 40 hours
Pipes A and B can fill a tank in 20 hours and 30 hours respectively while pipe C can empty the full tank in 40 hours. All are opened together, after 12 hours, pipe C closed. Find the time taken to fill the whole tank?
A. 16 hours 24 mins
B. 14 hours 48 mins
C. 15 hours 36 mins
D. 13 hours 40 mins
E. None of these
Sol:
Total units = LCM (20, 30 and 40) = 120 units
Pipe A can fill = 6 units/hr
Pipe B can fill = 4 units/hr
Pipe C can empty = 3 units/hr
1 hour work = 6 + 4 – 3 = 7 units/hr
12 hour work = 7 * 12 = 84 units/hr
Remaining work = 120 – 84 = 36 units
Remaining tank can be filled by pipe A and B in,
= > 36 / (6 + 4) = 3 3/5 hour
Total time taken by fill the tank
= > 12 + 3 3/5 = 15 3/5 hour (or) = 15 hours 36 mins