For a while now, my favorite problem like that has been finding a nice way to divide up a square into the seven triangle types. I love tangrams, and I like Pierre Van Hiele's mosaic puzzle even better. If you do too, stop reading right now and try this problem. It's fun and worth a surprising amount of thought. (For me, anyway.) Then suddenly this week, one of my little thumbnail sketches worked out. I don't know whether to be happy or sad. Being a geogebra nerd, I wanted to make a sketch of it, and that led to making a puzzle out of it.
You can print this picture of the pieces to try in real life, or try it with the Geogebra file or as a webpage. (A solution is an option on the file or webpage.)
But... now I'm left wondering what to think about in those rare extra moments. Then on Twitter, Justin Lanier (@j_lanier) tweets:
Had an insight in the shower this morning. Example: .717171... = .717171.../1 = .717171.../.999999... = 71/99 (!)Hmmm. Really? Maybe it's a coincidence, because 100 times .717171... minus the original leaves you 99... hmm. Would it work for .717171.../.6666... ? It does. Tweet back:
@j_lanier cool. So is .a_1 a_2...a_n repeating / .xxx... =a_1...a_n/xx...x (n times) for any x? Or divided by .b_1 b_2... b_m repeating ...Which connects to another problem (from Dave Coffey) I like thinking about: how many digits does it take 1/17 to repeat and how can you tell? In general?
OK. Deep breath. There's always more problems.