I believe September 1st is the only right answer.www.ddhw.com
www.ddhw.com
First of all, it could not be in June. Because if A does not know M, he is sure that B would not know the birthday. So if it was 6/7, no matter what, B knows it was in June. Since A denies that B knows the birthday in A's first sentence, he sends a signal to B that the month of the birthday definitely was not June. "A said If I don’t know, B doesn't know either". So A is sure B doesn't know. If the date is either 2nd or 7th, B would know the birthday under all possible conditions, then this condition prevents A from saying "If I don’t know, B doesn't know either”. Same logic here, it could not be in December either.www.ddhw.com
www.ddhw.com
So the only possible answers left for B were 3/4, 3/5, 3/8 and 9/1, 9/5. The month could not be 6 or 12. Then B said “I did not know before but now I know”. That tells us, it could not be 3/5 or 9/5, because if it was 3/5 or 9/5, B would still be confused by two 5’s. Then the only answers left for A are 3/4, 3/8, and 9/1. Since we know the month was Neither 6 or 12, so to B, if it was not on 6/4, it must be on 3/4. If it was not on 12/8, it must be on 3/8. If it was not on 12/1, it must be on 9/1. B said now he knows after A said the first sentence. All 3 possible answers were to choose one from two. Deny one answer will automatically push the right answer to the other. Could it be on 3/4 or 3/8 then? The answer is NO NO NO! To A, 3/4, 3/8, and 9/1 are all possible answers from B. However, remember, A finally said, “now I know it too”. If A was told the Month was 3, A would not able to tell the difference from 3/4 and 3/8, because either of them could be B's possible answer. If the month was 3, since we denied month was 6, so we can get 3/4, and we also denied month was 12, so we can get 3/8 as well. So if the month was 3, A could not say "Now I know the birthday". It is because A would have to get 2 possible answers from 4 choices. However, if A was told the Month was 9, and we denied the date was 5, A is sure to say "I know the answer". It is because A can choose one answer from two possible choices.
So A must know 9 was the month, and B must know 1 was the date.www.ddhw.com
Finally, 9/1 is and one and the only correct answer!
哈哈哈哈 O(∩_∩)O哈哈~ 好久不来了，不小心看了一眼自己主页，发现自动关联了自己以往发过的帖，点进这个看了一眼，笑个半死。。。敢情我当初还发过这么搞笑的东西啊，我自己完全不记得了 
雷达卡
发表于 2006-1-16 09:43:30
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千斤顶
发表于 2006-1-16 10:16:10
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