I was told a question during lunch at work and I haven't figured it out yet.

There are two empty jugs:

One five gallon jug

And

One three gallon jug

With an unlimited amount of water.

Using ONLY these two jugs

How can I get 4 gallons EXACTLY?

Fill the 3 gal jug and the pour it in to the 5 gal jug. Re-fill the 3 gal jug and start pouring into the 5 gal jug. When the 5 gal is full you have 1 gal left in the 3 gal jug. Empty the 5 gal jug completely, then pour the 1 remain gal from the small jug to the 5 gal. Refill the 3 gal jug then pour into the 5 gal jug. You now have 4 gals in a 5 gal jug.

Yep that's it