More Brain Busting

fill up 4 gallon add with 9 gallon = 13
fill up 4 gallon. fill up 4 gallon. fill up 4 gallon = 12
fill up 4 gallon. fill up 4 gallon = 8
fill up 9 gallon = 9
fill up 9 gallon. fill up 4 gallon with water from 9 gallon = 5
fill up 4 gallon = 4
fill up 9 gallon. fill up 4 gallon with water from 9 gallon (5). then pour into 4 gallon = 1