This is what you need:
-20 beer caps of ten different colors (10 pairs)
-a table or just a flat surface that can fit the caps in five columns of four caps with some gap between raws and columns.
How to play:
Mix the caps well and sort them out randomly on the table in five columns of four caps. You can swap two caps that are next to each other, left with right or top with bottom. Count your moves until you reach one of the configurations in which all the pairs of caps of the same color are formed.
Here is a sequence of three moves:
Got it? Now go for it... do your best!