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When is Cheryl’s birthday?

It’s been more than two years since I made a post tagged “brain teaser“. In the last few days I’ve seen a couple of interesting brain teasers which went viral on the internet, so it enticed me to posting one of them. It’s called

When is Cheryl’s birthday?

and it’s from some test. It is another exercise in lateral thinking. Here it goes:
Albert and Bernard just become friends with Cheryl, and they want to know when her birthday is. Cheryl gives them a list of 10 possible dates: May 15, May 16, May 19, June 17, June 18, July 14, July 16, August 14, August 15 and August 17. Cheryl then separately tells Albert the month of her birthday and Bernard the day of her birthday. The conversation goes: Albert: “I don’t know when Cheryl’s birthday is, but I know that Bernard does not know either.” Bernard: “At first I didn’t know Cheryl’s birthday, but now I know!” Albert: “Well, then I now also know Cheryl’s birthday!”
And now you know it, too… or do you? 🙂
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One Comment

  1. Posted May 11, 2015 at 8:27 pm | Permalink

    Cheryl’s birthday is July 16th. It cannot be in May or June, otherwise Albert could not be sure that Bernard didn’t already know (18th or 19th would give Bernard the answer). Now Bernard knows it is in July or August, and either the 15th, 16th, or 17th would make him certain of the date. Since Albert now knows it is one of those three days, and says he knows the exact date, it must be July 16th.

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