If you already have trouble remembering the birthday dates for your friends, relatives, or (God help you) your significant other or children, then this math/logic puzzle isn't for you. That's because it asks the very simple question, "When is Cheryl's birthday?"
This problem came up in the Singapore and Asian Schools Math Olympiads contest. A TV presenter put it online and since then it's spread like crazy as everyone tries to figure it out. So, can you do it?
Here's the full question:
Albert and Bernard just became 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 them tells Albert and Bernard separately the month and the 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 [sic.] 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?
Aside from the fact that Cheryl sounds like a terrible friend, the entire problem isn't phrased quite as clearly as it should be. I'll help you out a bit by clarifying that Albert knows the month and Bernard knows the day. Also, Albert and Bernard are speaking out loud to each other there at the end.
So, do you think you have the answer?