article: It was the maths problem designed for 14-year-olds that baffled people around the world. For those who did not manage to work out the cryptic clues that were designed to lead them towards the fictional Cheryl's birthday, then the answer was July 16. Those who were able to reason their way to this answer followed a series of logical steps that allowed them to rule out the other dates given as part of the question. The question, 'So when is Cheryl’s birthday?' was one of 25 questions set in the Singapore and Asian Schools Math Olympiad. At first, it appears impossible to answer without more information but pictured is the method used to work it out . The question, 'So when is Cheryl’s birthday?' was one of 25 questions set in the Singapore and Asian Schools Math Olympiad. It asked: 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. The puzzle asked: 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? Albert said: 'I don’t know when Cheryl’s birthday is, but I know that Bernard does not know too. Bernard said: 'At first I don’t know when Cheryl’s birthday is, but I know now.' Albert said: 'Then I also know when Cheryl’s birthday is.' To reach the answer, it is possible to work through the information both men known to rule out nine of the dates in a number of steps. First, we know Cheryl has already told Albert the month of her birthday, and Bernard the day. Each of the men does not know what the other has been told. So, for Albert to be 'certain' that Bernard cannot know the answer - as suggested in the first statement he makes - we can deduct that the birthday cannot possibly be in May or June. This is because in the months of May and June there are numbers (dates) that only occur once across the four months - namely May 19 and June 18. If Albert had been given May or June as the month, there is no way he could be sure Bernard did not already know the birthday as  Bernard might have been the number 18 or 19. For Albert to be 'certain' that Bernard doesn't know, Albert must have been given a month that does not contain one of these 'unique' dates - i.e. July or August. The problem was posted on Facebook by ‘Hello Singapore’ television presenter Kenneth Kong, and went viral as people posted 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 (stock image of exam room shown) Albert's disclosure now gives Bernard the clue he needs to work out the birthday for himself. Bernard only knows the number of Cheryl’s birthday, but from Albert’s statement he has now also ruled out both May and June. This is because he realises Albert has ruled out May and June because of the 'single number' aspect above. As Bernard says he knows the date, we can whittle it down further to three dates by ruling out the numbers that appear in duplicate. If Cheryl had told Bernard that her birthday fell on the 14th of the month, then he could not have worked out the date at this stage. However, as he states that he now knows the date, we can rule out July 14 or August 14. This leaves just three dates to chose from - July 16, Aug 15 and Aug 17. Following Bernard's statement, Albert is then apparently also able to deduce the date of Cheryl's birthday. This means her birthday must be the only remaining date in the month he was originally told. Given that there are two dates left in August and one in July, it has to be the July date. So the answer is July 16. Organisers of SASMO said the question was set to filter out the most intelligent of participants. This year around 28,000 students from countries across the world including Singapore, China and the UK took the test . The problem was posted on Facebook by ‘Hello Singapore’ television presenter Kenneth Kong, and went viral as people posted 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. This year around 28,000 students from countries across the world including Singapore, Thailand, Vietnam, China and the UK took the test. Henry Ong, executive director of SASMO, told Mothership.sg: '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.' Of course, perhaps the more important question is whether Cheryl deserves a birthday gift at all after putting us through all of this.
highlights: Maths problem set for 14-year-olds left people around the world baffled .
  Question uses logical reasoning to rule out all of the dates apart from one .
  It was set in the Singapore and Asian Schools Maths Olympiads (SASMO)
  Teaser generated furious online debate - but correct answer was July 16 .
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