article_snippet.sent: It asked: Albert and Bernard just became friends with Cheryl, and Albert and Bernard want to know when Cheryl is.
article_snippet.sent: Cheryl gives Albert and Bernard a list of 10 possible dates: May 15, May 16, May 19, June 17, June 18, July 14, July 16, August 14, August 15 and August 17.
article_snippet.sent: Cheryl then tells Albert and Bernard separately the month and the day of Cheryl respectively.
article_snippet.sent: The puzzle asked: Albert and Bernard just became friends with Cheryl, and Albert and Bernard want to know when Cheryl is.
article_snippet.sent: Cheryl gives Albert and Bernard a list of 10 possible dates.
article_snippet.sent: Cheryl then tells Albert and Bernard separately the month and the day of her birthday respectively.
article_snippet.sent: Albert said: 'I don’t know when Cheryl’s is, but I know that Bernard does not know too.
article_snippet.sent: Bernard said: 'At first I don’t know when Cheryl’s is, but I know now.'
article_snippet.sent: Albert said: 'Then I also know when Cheryl’s is.'
article_snippet.sent: First, we know Cheryl has already told Albert the month of Cheryl , and Bernard the day.
article_snippet.sent: So, for Albert to be 'certain' that Bernard cannot know the answer - as suggested in the first statement Bernard makes - we can deduct that Cheryl’s birthday cannot possibly be in May or June.
article_snippet.sent: If Albert had been given May or June as the month, there is no way Albert could be sure Bernard did not already know Cheryl’s birthday as  
article_snippet.sent: Albert's disclosure now gives Bernard the clue Bernard needs to work out Cheryl’s birthday for Bernard.
article_snippet.sent: Bernard only knows the number of Cheryl’s birthday, but from Albert’s statement Bernard has now also ruled out both May and June.
article_snippet.sent: If Cheryl had told Bernard that Cheryl birthday fell on the 14th of the month, then Bernard could not have worked out the date at this stage.
article_snippet.sent: Following Bernard's statement, Albert is then apparently also able to deduce the date of Cheryl's birthday.