I saw this question on Facebook:
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 16 19
June 17 18
July 14 16
August 14 15 17
Cheryl then 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 didn't know when Cheryl's birthday is, but I know now.
Albert: Then I also know when Cheryl's birthday is.
When is Cheryl's birthday?
There is an official solution which is explained in the link below, but I don't understand the logic.
July 16, as explained here. https://www.facebook.com/kennethjianwenz/posts/386479228197631
What is wrong with the logic in the answer I posted below (I put it in spoilers if others want to try)?