Here's a fun puzzle explained to us by math writer Alex Bellos (but invented by mathematician Henry Ernest Dudeney) that you can try with six coins. First line them up like this: 
Now see if you can arrange them in a circle with only three moves. The two rules: you can slide them but not pick them up, and you must move them to a position where they are touching two other coins.
Here is a video explaining the rules a bit more, but spoiler alert: don't go past 2:37 unless you want to see how it's done.
https://youtu.be/_pP_C7HEy3g
