Put three piles of toothpicks (or matches, crayons, etc) on a table – one pile with 11, one with 7, and one with 6. The goal is to finish with 8 matches in each pile, but you may only add to a pile the number of matches it already contains, and all the matches must come from one other pile. For example if a pile holds 6 matches you may add 6 to it, no more, no less. You have 3 moves. Good luck!
(I can’t find where I got this puzzle from – if you know the original let me know in the comments!)