A cistern can be filled with water by a pipe in 5h and it can be emptied by another pipe in 4 h. When the cistern is full, both the pipes are opened together. Calculate the time in which the cistern will be emptied.
[SSC CGL 2002]
Explanation
According to the above given formula, if pipe A can comletely fill a tank in x hours and pipe B can empty the same tank in y hours, then the time taken to fill the tank when both the pipes are opened simultaneously is hours.
So,
Therefore, the tank will be filled in 20 hours when both the pipes are opened simultaneously.
Hence option C is correct.
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