I also like ones like the classic: you have a water source, and you want to put 4 units of water into a target container, but you only have a measuring container of size 5 and one of size 3, what do you do?
Fill the three empty it into the five. Fill the three use it to fill the five. Pour the remaining one out into the target. Fill the three add it to the target = 4
my solution is loop-friendly:
fill the 5, use it to fill the 3, use the rest to fill the 4, repeat.
(EDIT: forgot the smile )