Brain Teaser: Follow the Pattern

One of my blog readers mailed me this puzzle earlier this year.  Warning: it's a tough one!  

I love getting mail at school that isn't people trying to sell me stuff...







He even provided me with an answer that was hidden so I couldn't cheat.


I pondered this puzzle for WEEKS.  I showed it to my sister.  She was stumped, too.  I showed it to some students who happened to be hanging out in my room at lunch.  We could not figure it out.

I actually never ended up figuring it out myself.  I tweeted about trying to solve it, and someone tweeted back with the answer to the puzzle even though I had specified "no spoilers, please."

After seeing the answer, I'm not sure if I would have ever actually come up with the answer myself.  But, I guess I'll never know now.  It's a good reminder to me to not give the answers away too quickly to my students.

Enjoy.  :D

And, please, no spoilers in the comments for those who want to play along.