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Title:

Albert (a) and Bernard (b) have just made friends with Cheryl. They want to know Cheryl's birthday. Cheryl finally gave them ten possible dates:

May 15, May 16, May 19.

June 17, June 18

July 65438, 2004

August 14, August 15, August 17.

Cheryl told A and B the month and date of her birthday respectively.

A: I don't know Cheryl's birthday, but I know B won't know either.

B: I didn't know Cheryl's birthday at first, but now I do.

Then I also know Cheryl's birthday.

The topic asks students to analyze several conversations between two young people and finally infer Cheryl's birthday.

The analysis is as follows:

1, Albert said he didn't know, and Bernard certainly didn't know, which means the month is not May or June. Because if Bernard knew the date was 19 or 18, he would immediately know that his birthdays were May 19 and June 18, because these two days were separated. So now there are only July and August left in June.

Bernard said that he didn't know at first, but now he knows, which means that the date is definitely not 14. Because 14 is July and August, even if we know it is 14, we still don't know what month it is, and we are still not sure. He can confirm that the dates are 15, 16 and 17.

Albert said that he knows now, which means that the month is July. Because if he hears August, Bernard knows his birthday, but he is still not sure what day it is. Since he said he knew, it means that the month must be July.

To sum up, the date must be1July 6.

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