Puzzle #22: Cheryl’s birthday
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 then tells Albert the month of her birthday and Bernard the day of her birthday separately. Then the following conversation takes place:
Albert: I don’t know when Cheryl’s birthday is, but I know that Bernard also does not know.
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?
You’ll be relieved to hear that the solution does not involve 80-digit numbers. It does, however, require some careful logic.
Find the solution at the bottom of this page.
