How to solve it! Cheryl's birthday puzzle part two: Denise's revenge
by Alex Bellos from on (#9RH8)
The last word on Albert, Bernard, Cheryl and Denise. With workings.
Guzzlers, how did you get on?
Let me first restate the problem. Albert, Bernard and Cheryl became friends with Denise, and they wanted to know when her birthday is. Denise gave them a list of 20 possible dates.
Albert: I don't know when Denise's birthday is, but I know that Bernard does not know.
Bernard: I still don't know when Denise's birthday is, but I know that Cheryl still does not know.
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