It’s the question that has left adults around the world scratching their heads – and it comes from a math paper for 14-year-olds in Singapore.
The logical reasoning poser – So when is Cheryl’s birthday? – was posted on Facebook by Hello Singapore television presenter Kenneth Kong, and went viral as people made public their various solutions to the problem.
It was set for 14-year-olds in the Singapore and Asian Schools Math Olympiads (SASMO), which were held on April 8 and this year around 28,000 students from countries across the world including Singapore, Thailand, Vietnam, China and the UK took the test.
But since it was put online it has been baffling just about everyone.
Here’s the question:
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, 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?
Try to work it out yourselves. To check whether you can compete with the 14-year-olds, follow this LINK to Neil Baldacchino’s explanation in the Study Room for the correct answer.
Or follow this: