OMG How's this possible
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 and Bernard separately the month and the day of her birthday respectively.
Then Albert said: I don’t know when Cheryl’s birthday is, but I know that Bernard does not know too.
Bernard: At first I don’t know when Cheryl’s birthday is, but I know now.
Albert: Then I also know when Cheryl’s birthday is.
So when is Cheryl’s birthday?
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1 solution
If Cheryl's birthday was either in May 19 or June 18, Bernard would know at first when Cheryl's birthday is, but at first he doesn't know when it is. Albert doesn't know when Cheryl's birthday is, but he knows that Bernard doesn't know too, so Cheryl's birthday is neither in May nor June. Then, Bernard says "At first I don't know when Cheryl's birthday is, but I know now", so Cheryl's birthday is neither in July 14 nor August 14. Finally, Albert also know when Cheryl's birthday is, so it is not in August. The answer is July 16