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etherdome

Cheryl's Birthday

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A question on a standardized math test in Singapore has gone viral. The question goes like this:

Albert and Bernard just became friends with Cheryl. They want to know Cheryl's birthday. Cheryl gives them a list of possible dates.

May 15 May 16 May 19

June 17 June 18

July 14 July 16

Aug 14 Aug 15 Aug 17

She also tells Albert the month of her birthday and Bernard the day (number ) of her birthday. The question continues with a dialogue between Albert and Bernard.

Albert: I don't know the answer, but I know that Bernard does not know the answer either.

Bernard: Well, I did not know the answer, but based on what you just said, I know the answer now.

Albert: Based on what you just said, I now know the answer.

Keep in mind that this is a logic question and that you have to accept that everyone tells the truth and that sometimes the situation can be unrealistic. For example, in this question, Albert and Bernard do not simply share their information freely and go about their lives.

After the obligatory jokes about Albert's and Bernard's motivations, give this question some thought and try to figure out Cheryl's birthday. I had the wrong answer because I made an early heuristic mistake.

Good luck.

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