Remember the card trick on YouTube , where the poster begged someone to explain how it worked? Ana and her son Julio figured it out and the explanation is here , in Ana's own handwriting.
Now they've done another one. She and her son loved a puzzle Will Shortz used on his regular feature on a recent Weekend Sunday, on NPR. It's simple (but not that easy). Here's the puzzle: 
Using only standard mathematical symbols (x, ., /, ,  etc.) make three nines (9, 9, and 9) equal 20. 
Ana was...