Pipe A can fill a tank in 12 hours and Pipe B can fill the tank in 18 hours. If both the pipes are opened on alternate hours and if pipe B is opened first, then in how much time (in hours) the tank will be full?
1-hour Efficiency of pipe A: 1/12
1-hour Efficiency of pipe B: 1/18
If both opened together, work done in 2 hours: 1/18 + 1/12 = 5/36
After 14 hours, work done = 5 × 7/36 = 35/36.
Work left = 1 – 35/36 = 1/36. This work will be done by pipe B in h hours.
⇒ h/18 = 1/36
⇒ h = 1/2Therefore, total time = 14.5 hours