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Water cans puzzle

Water cans puzzle is very common puzzle asked in interviews.somewhere or the other you must have encountered with this type of puzzles.

Puzzle :

 Sam is on a treasure hunt and on his way to find out the treasure he reached at river where he encountered with the next clue which will further show him the path towards the treasure.Now for the next clue he saw two cans,one is of 9 gallon and another is of 4 gallon both are empty initially and a balance with a note on it "Exactly six gallons of water will show you the way".Now Sam has to measure exactly six gallons of water to get the map for further search.Assume that Sam can transfer water from one can to another and also throw water if it is required.How will he measure exactly 6 gallons of water?

Solution :

 Obviously you cannot measure 6 gallons of water in a 4 gallon can.So you have to take 6 gallons of water in a 9 gallon can and keep it on balance.

Here are the steps sam will follow :-

1) Sam will first pour water in 9 gallon can completely from the river.
2) Now he will transfer 4 gallons of water in 4 gallon can leaving the 9 gallon can with 5 gallons water.
3) He will now empty the 4 gallon can by throwing water from it.
4) Again he will transfer 4 gallon of water from 9 gallon can leaving 1 gallon of water in 9 gallon can.
5) He will now again empty 4 gallon can and transfer remaining 1 gallon of water into 4 gallon can leaving 9 gallon can empty.
6) Now he will again fill the 9 gallon can completely with water from the river.
7) Finally he will pour rest 3 gallon of water in 4 gallon water making it completely filled and leaving 6 gallon of water in 9 gallon can and put it on a balance to get the map.

PS - Remember water can puzzle from the movie Die-Hard 3 :-)

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