* Fill up 5 gallon jug.
* Fill up 3 gallon jug from 5 gallon jug.
* Empty 3 gallon jug.
* Pour 2 gallon remaining in 5 gallon jug into 3 gallon jug.
* Fill up 5 gallon jug.
* Fill up 3 gallon jug with 5 gallon jug.
=> 3 gallon jug is full and 4 gallon remains in 5 gallon jug.