# Harder Cheryl's Birthday

Logic Level 4

Albert, Bernard, and David just became friends with Cheryl, and they want to know when her birthday is. Cheryl gives them a list of 16 possible dates.

May 15, May 16, May 19

Jun 17, Jun 18, Jun 20, Jun 22

Jul 15, Jul 16

Aug 14, Aug 20, Aug 22

Sep 14, Sep 16, Sep 17, Sep 20

Cheryl tells Albert and Bernard separately the month and the day of her birthday, respectively. She then chooses one particular date from the list and tells David, and makes it known to all that the chosen date has a different day and month from her birthday.

Albert: I don’t know when Cheryl’s birthday is, but I know that Bernard does not know too.

Bernard: I did not know when Cheryl’s birthday is. And now I still don't.

Albert: I still don't know when Cheryl's birthday is. Having said that, I am sure David still does not know.

David: I knew neither the day nor the month right before Albert said his last sentence, but after he did, now I know what month it is.

Bernard: I did not know when Cheryl’s birthday is right before Albert said his last sentence, but after he did, now I know when Cheryl’s birthday is.

David: Then I also know when Cheryl’s birthday is.

Albert: Now I know too.

So when is Cheryl’s birthday?

Note: Last sentence refers to “Having said that, I am sure David still does not know too.”

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