Pipe A can empty filled tank in 28 hours while Pipe B can fill the same tank, when
empty, in 35 hours. If alternately Pipes A and B are turned on for an hour each time, starting when the tank is full, how long will it take to empty the tank?
LCM(28, 35) = 140 litres is the total capacity of tank.
A pipe empties 5 liters in 1hour and Pipe B fills 4 liters in 1hour.
In 2 hours A and B pipes empties 1 liter.
[ It can understand by,
A’s 1 hour work and B's next hour( 2nd hour) work,
Here,( - ve sign indicates emptying the tank)]
From this we can easily conclude that,
Every 2 hours empties both pipes together 1 liter.
For emptying full tank of 140litre takes,
If pipe A was started emptying the tank first
Then answer will like this,
For emptying of 135 liters takes time 2x135 = 270 hours and remaining 5liters emptied in 1hour by pipe A
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