May 15, May 16, May 19.
June 17, June 18
July 65438, 2004
August 14, August 15, August 17.
Cheryl told Albert the month and Bernard the date of her birthday.
Then Albert made the following statement: I don't know Cheryl's birthday, but I know Bernard won't know either.
Bernard replied: I didn't know Cheryl's birthday at first, but now I know.
Albert also replied, now I know Cheryl's birthday.
Q: When is Cheryl's birthday?
Answer:
1, in 10 days, only 18 and 19 appeared once. If Cheryl's birthday is 18 or 19, Bernard who knows the date can guess the month. He must know when Cheryl's birthday is. Albert determined that Bernade didn't know Cheryl's birthday, so he inferred that it wouldn't be in 18 or 19, and then decided that it wouldn't be in May or June when 18 or 19 appeared. So her birthday must be July or August.
2. According to bernal, only 14 appeared twice in the remaining five days in July and August. If Cheryl told bernal that her birthday was 14, it would be impossible for bernal to guess her birthday from Albert's words. So 14 is excluded. Now the only possibilities are July 16, August 15 and August 17.
After Bernade's speech, Albert also knew Cheryl's birthday, which indicated that the birthday month could not be in August. Because there are two possible days in August, and there is only one possibility in July.
So the answer is July 16.