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Answer to Riddle #22: The 3 & 5 Litre Die Hard Water Puzzle

22. You have a 3 and a 5 litre water container, each container has no markings except for that which gives you it's total volume. You also have a running tap. You must use the containers and the tap in such away as to exactly measure out 4 litres of water. How is this done?

You might remember this puzzle from Die Hard with a vengeance where Bruce Willis and Samuel L. Jackson have to diffuse a bomb by placing 4 gallons of water on a set of scales...

illustrate die hard water puzzle Before reading the answer can I interest you in a clue?

There are two ways to solve this, maybe the question could be modified to say the 5 litre can doesn't fit under the tap...

Number 1
  • Fill the 5 litre can from the tap
  • Empty the 5 litre can into the 3 litre can - leaving 2 litres in the 5 litre can.
  • Poor away the contents of the 3 litre can.
  • Fill the 3 litre can with the 2 litres from the 5 litre can - leaving 2 litres in the 3 litre can.
  • Fill the 5 litre can from the tap.
  • Fill the remaining 1 litre space in the 3 litre can from the 5 litre can.
    Leaving 4 litres in the 5 litre can.
Number 2
  • Fill the 3 litre can from the tap.
  • Empty the contents of the 3 litre can into the 5 litre can.
  • Fill the 3 litre can from the tap.
  • Empty the contents of the 3 litre can into the 5 litre can. - Leaving the 5 litre can full and 1 litre in the 3 litre can.
  • Poor away the contents of the 5 litre can
  • Poor the 1 litre from the 3 litre can into the 5 litre can.
  • Fill the 3 litre can from the tap.
  • Empty the contents of the 3 litre can into the 5 litre can.
    Leaving 4 litres in the 5 litre can.


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