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When is Cheryl’s birthday? This maths question is melting our brains

A maths problem set for teenagers taking the Singapore and Asian Schools Maths Olympiads (SASMO) has gone viral for one reason. It’s impossible.*

“When is Cheryl’s birthday?” is the question and the answer has proved impossible for the majority of us to fathom out. Set as a maths problem in an exam paper to test the logical reasoning skills of 14-year-olds in Singapore, it has been shared online thousands of times as people across the world attempt to figure it out.

On April 8 around 28,000 students from countries across the world, including Singapore, Thailand, Vietnam, China and the U.K. took the test.

Henry Ong, executive director of SASMO, told “Being Q24 out of 25 questions, this is a difficult question meant to sift out the better students. SASMO contests target the top 40% of the student population and the standards of most questions are just high enough to stretch the students.”

More: The colour-changing dress was another viral sensation that had us all flummoxed

If you haven’t given it a go, and think logical reasoning is up there as one of your top qualities, here’s the question in full. Warning: your brain may actually hurt after reading this.

Albert and Bernard just became 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 tells Albert and Bernard separately the month and the day of her birthday respectively.

Albert: I don’t know when Cheryl’s birthday is, but I know that Bernard does not know too.

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

Albert: Then I also know when Cheryl’s birthday is.

So when is Cheryl’s birthday?

*Actually, it’s not impossible. It’s July 16. But we still don’t know how to work it out. Cheryl, we might know when your birthday is but there’s no way you’re getting a present after putting us through all that.

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