For the last couple of days, I have been playing around with this geometry puzzle. If you have a student in geometry or higher math, I recommend you print out the original post (but not the comments — it’s no fun when someone gives you the answer!) and see what he or she can do with it.
[MathNotations offers many other puzzles for 7-12th grade math students. While you are at his blog, take some time to browse past articles.]