By now I'm sure everyone has run into the math puzzle where Albert and Bernard try to deduce Cheryl's birthday, which is all over social media, and even traditional media! If you don't know what I'm talking about, see e.g. this Washington Post article (or the transcript below):
It's a nice logic puzzle, and I'm delighted to see any math fall into general public consumption, but to me it feels like hundreds of other logic puzzles. As someone who has spent lots of time unsuccessfully trying to get people into math problems, I wonder what the trick is with this one. Whatever it is, can we use it to design problems that students will be naturally puzzled by?
A transcript of the puzzle:
Albert and Bernard just become friends with Cheryl, and they want to know when her birthday is. Cheryl gives them a list of 10 possible dates.
May 15, May 16, May 19 June 17, June 18 July 14, July 16 August 14, August 15, August 17
Cheryl then tells Albert and Bernard separately the month and tha day of her birthday respectively.
Albert: I don't know when Cheryl's birthday is, but I know that Bernard does not know too.
Bernard: At first I don't know when Cheryl's birthday is, but I know now.
Albert; Then I also know when Cheryl's birthday is.
So when is Cheryl's birthday?