Albert and Bernard have 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 the month, and Bernard the day of her birthday.

Albert: “I don’t know when Cheryl’s birthday is, but I know that Bernard doesn’t know either.” Bernard: “At first I didn’t know when Cheryl’s birthday was, but now I know.” Albert: “Then I know it too.”