Watching "Die Hard With a Vengeance" with Daddy. She solved the bottle riddle (since she's quite familiar with bottles as of now). How do you get exactly 4 gallons from one 3 gallon bottle and one 5 gallon bottle?

You fill up the five gallon bottle and pour it into the 3 gallon bottle. That leaves 2 gallons in the 5 gallon bottle. Empty the 3 gallon one and pour the 2 left in the 5 into the 3 gallon bottle. Fill up the 5 gallon bottle yet again, and then fill up the 3 gallon with the liquid from the 5 gallon. This will leave 4 in the 5 gallon bottle. There is an alternative solution, involving filling up the 3 gallon bottle twice at the get-go....