There is a 5 gallon and a 3 gallon bottle. You also have a hose with unlimited water. How are you gonna make the 5 gallon have 4 gallons using your items?
(You don't know the exact dimensions of a gallon)
You fill the five gallon up and pour it into the 3 gallon. The dump the 3 gallon out and pour what was left in the 5 gallon into the 3 gallon so that you have 2 gallons in the 3 gallon. Then fill the 5 gallon up and pour it into the 3 gallon to fill it up. Now you have 4 gallons in the 5 gallons.