I have a 5 gallon jug and a 3 gallon jug, and a pool of water. I need 4 gallons of water exactly for reasons best known to myself. Using these tools, how do I get 4 gallons of water accurately?

First, you compare the sizes of the two jugs together. If you put the 3 gallon jug against the 5 gallon jug, it can be assumed that of the remaining space, half of it is a gallon. Mark it off with a pen, then start taking water from the pool. Using the 3 gallon jug, pour water into the 5 gallon jug. Then divide the 3 gallon jug into thirds, using aforementioned pen. Fill it with water up to the first mark and pour that water into the 5 gallon jug. You will have 4 gallons.

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