Albert and Bernard just friends with Cheryl and they wanted to know his birthday. Cheryl then give 10 options, namely:
May 15, 16 Mei, May 19
June 17, 18 Juni
July 14, 16 of July,
August 14, 15 August, and August 17
Cheryl later told Albert and Bernard separately on the month and date of his birthday sequentially.
Albert and Bernard then made a statement:
Albert: I do not know when Cheryl's birthday, but I'm sure Bernard does not know well.
Bernard: At first I did not know Cheryl's birthday, but I now know.
Albert: It means I also know Cheryl's birthday.
So when Cheryl's birthday?