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# Water Jug Riddle

You have a 3-litre jug and a 5-litre jug, and as much water as you need. How do you measure out exactly 4 litres using only these two jugs?

This is a classic logic puzzle, sometimes used in finance and engineering interviews many years ago. It also was featured in the movie Die Hard with a Vengeance!

#### Solution

1. Fill up the 3-litre jug, and pour it all into the 5-litre jug
2. Fill up the 3-litre jug again, and use it to fill up the 5-litre jug – the 3-litre jug now has exactly 1 litre left
3. Empty out the 5-litre jug
4. Pour the 1 litre from the 3-litre jug into the 5-litre jug
5. Fill up the 3-litre jug, and pour it all into the 5-litre jug (which already had 1 litre in it) – the 5-litre jug now has exactly 4 litres in it!

Alternate solution:

1. Fill up the 5-litre jug, and use it to fill up the 3-litre jug. The 5-litre jug now has exactly 2 litres left.
2. Empty out the 3-litre jug
3. Pour the remaining 2 litres in the 5-litre jug into the 3-litre jug.
4. Fill up the 5-litre jug again, and use it to fill up the remaining capacity of the 3-litre jug – the 5-litre jug now has exactly 4 litres in it!