I need a 4 gallon bucket the problem is I only have a 5 gallon bucket and a three gallon bucket.
How do i get 4 gallons on the dot?

Place 3 gallons into the 5 gallon bucket by using the 3 gallon bucket then finish filling up the 5 with the full 3 gallon bucket which will leave u with 1 gallon in the 3 gallon. Then empty the 5 pour in the 1 gallon into the 5 gallon and fill the 3 gallon and pour into 5 gallon to get 4 gallons.