# Cheryl’s Birthday Problem

We all know by now Singapore Math is not easy, but here is the viral Singapore Math problem that took the world by storm!

Question:

Albert and Bernard just became friends with Cheryl, and they want to know when her birthday is. Cheryl marks 10 possible dates: May 15, May 16, May 19, June 17, June 18, July 14, July 16, August 14, August 15, or August 17.

Then Cheryl tells Albert the month of her birthday, but not the day. She tells Bernard the day of her birthday, but not the month. Then she asked if they can figure it out.

Albert: I don’t know when Cheryl’s birthday is, but I know Bernard doesn’t know either.

Bernard: At first I didn’t know when Cheryl’s birthday is, but now I know.

Albert: If you know, then I know too!

When is Cheryl’s birthday?

There is a nice Numberphile video about it too.

Do give it a try! (The fun is in trying to solve the question)

Also, another fun part is sending this question to your friends!

Also see: Meet the mathematics lecturer behind ‘Cheryl’s birthday’ puzzle – See more at: http://www.straitstimes.com/news/singapore/more-singapore-stories/story/meet-the-mathematics-professor-behind-cheryls-birthday-p#sthash.qKZZtwpk.dpuf

To be honest, though Cheryl’s birthday puzzle is difficult, there are more challenging logic puzzles around. For a good challenge (and good practice), check out Puzzle Baron’s Logic Puzzles. It is a very good practice for children gearing up for Math Olympiad since they love to test logic questions in Math Olympiad.

## Author: mathtuition88

Math and Education Blog

## 9 thoughts on “Cheryl’s Birthday Problem”

1. abyssbrain says:

For me, that logical puzzle was not that difficult compared with the others out there, but I may just be biased since I like to solve logic puzzles a lot, so I’ve already encountered several weirder ones. Though admittedly, the Cheryl’s bday problem would be very difficult for people who are not used to solving complicated logic puzzles.

Liked by 1 person

1. Yeah, you are right. I guess that is part of its popularity, it is baffling but actually solvable if one thinks long enough.

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1. Well, it doesn’t just take time; it takes the insight that you can deduce what someone knows from their declarations about what they could or couldn’t know. That sort of turning meta-information into information is a common enough trick for this sort of logic puzzle, but it’s a big leap if you haven’t seen the trick before.

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2. That’s correct. I guess the appeal of the question lies here.

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2. Nice word problem – too hard for me though ðŸ™‚ I had to look up the answer! I’d like to get a puzzle book for my 4th graders – would the book you recommend be good for them or possibly too hard?

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