text: The riddle of the water tank or the tank issue is one of the content in the book " The nine chapters on mathematical art " one of the oldest books math China, dating back to the period of Zhou Dynasty.
  
  Riddle:
  We have a water tank of 48 m3 capacity with two filling pipes and drain .
  The first filler pipe open one would take 12 hours to fill the tank .
  The second filler pipe open only take six hours to fill the tank.
  With fully fueled and the two filling lines closed , the discharge pipe would take eight hours to remove all the water and leave the empty tank.
  
  Question:
  If we start from the empty tank and open the three pipes how long it would take to fill the tank?
  
  See the solution to the riddle