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I think there are two solutions. The video in the link gives one, the other is June 17. Supposing Albert knows the day, his statement eliminates June 18 and M
by codeonfire 11y ago
I think there are two solutions. The video in the link gives one, the other is June 17. Supposing Albert knows the day, his statement eliminates June 18 and May 19. Bernard claims to know the answer, which can only be June 17. Albert does the same logic and reaches the same conclusion.
- pango 11y agoI am not sure that is true. If albert knows bernard doesn't know the day at the beginning, it can't be june since the number 18 would be uniquely identifiable as june 18 for bernard from the beginning.
- deciplex 11y agoBut, Albert doesn't know the day at first. If Cheryl had told him "June" he would not know that Bernard does not know her birthday.
- recursive 11y agoIf there are two solutions, then there are zero solutions.
- myhf 11y agoAlbert doesn't know the day. The problem states that Albert and Bernard know the month and day respectively.
- shkkmo 11y agoAlbert does not know the day, he knows the month. Alberts statement eliminates all June and May dates because he says he "Know thats Bernard doesn't know" before Bernard says he didn't know.
- sago 11y agoYour second solution depends on interpreting the "Albert knows Bernard doesn't know" to mean that Bernard told (or otherwise signalled to) Albert that he doesn't know, rather than Albert deducing that Bernard couldn't know. There was a detailed rebuttal of this interpretation by the folks who set the original question. But it is easy to claim "that's not what I meant!" Actually being precise about what you mean is fiendishly difficult. I recommend Imre Lakatosh's excellent book on proofs "Proofs and Refutations" - its short, and thoroughly dismantles the early 20th century ideas that math is somehow a precise conceptual structure independent of language ambiguities. Or put another way: with enough eyeballs, all language is ambiguous.