This genre of logic puzzles is baffling in large part because people rarely act this way. The puzzles also have built-in assumptions — everyone is truthful, for instance and no one gets offended and walks off when strangers insist on making basic communication so complicated. Students who compete in math competitions are generally familiar with the conventions of logic puzzles, but people who have not taken a math class for more than a decade generally say, “Huh?” 
 
 This puzzle is particularly convoluted. Why don’t Albert and Bernard just blurt out what Cheryl has told them? Why is Cheryl so coy about revealing the month and day, but not year, of her birthday? What else is Cheryl trying to hide? 
 
 But if you are willing to play, here’s how the logic unwinds. 
 
 It helps to put the list of 10 dates into table form: 
 
 Image 
 
 Now let’s examine what Albert and Bernard say. Albert goes first: 
 
 I don’t know when your birthday is, but I know Bernard doesn’t know, either. 
 
 The first half of the sentence is obvious — Albert only knows the month, but not the day — but the second half is the first critical clue. ||||| Image copyright Kenneth Kong Image caption The logic question posted by Mr Kong is now known as 'Cheryl's Birthday' 
 
 A school maths question posted on Facebook by a Singaporean TV presenter has stumped thousands, and left many asking if that's really what is expected of Singaporean students. 
 
 The question asks readers to guess the birthday of a girl called Cheryl using the minimal clues she gives to her friends, Albert and Bernard. 
 
 Cheryl's Birthday was initially reported to be an examination question for 11-year-olds. 
 
 Students stressed by tough examinations is a perennial issue here, and Cheryl's Birthday reignited concerns that the education system was too challenging. 
 
 Image copyright facebook 
 
 But it later emerged it was for students aged about 15 taking part in last week's Singapore and Asian Schools Math Olympiads (Sasmo). 
 
 Organisers said the test was aimed at the top 40% and aimed to "sift out the better students", adding it was "important to clarify so that Singapore parents will not start to worry so much". 
 
 Image copyright Twitter 
 
 Kenneth Kong, who first posted the problem, told the BBC: "It's a really difficult question for younger kids, so that's why people were so shocked at first... but now that people know it's for older students, they just think it's quirky." 
 
 Media playback is unsupported on your device Media caption Author and mathematician Alex Bellos demonstrates how to solve the problem 
 
 Sasmo's executive director Henry Ong defended the question, saying there was "a place for some kind of logical and analytical thinking in the workplace and in our daily lives". 
 
 Image copyright Twitter 
 
 "We are not saying this problem is for every student... But if these kind of problems can be used to stretch the better students to sharpen their analytical power, why not?" 
 
 The question, which has been shared around the world, sparked a Twitter hashtag #cherylsbirthday and even a music track. 
 
 "After spending so much time together, thinking of Cheryl's birthdate, Albert and Bernard soon fell in love with each other and forgot all about Cheryl," said Elfy Bianca Hassan on Mr Kong's page. 
 
 "Dump her. Find other girls," suggested Nicholas Lim. 
 
 Image copyright Twitter 
 
 Others took umbrage at the wording. "I hope people picked up that the person who set the question needs to go for English grammar classes - there are at least two grammar errors," said Clarence Singam-Zhou. 
 
 So when is Cheryl's birthday? 
 
 The answer is 16 July, said Sasmo which posted the correct solution. 
 
 Image copyright Twitter 
 
 Sasmo also dismissed an "alternative solution" which resulted in 17 August. 
 
 Their rejection was that "since Bernard did not say that he does not know when Cheryl's birthday is, then how did Albert know that Bernard does not know?" 
 
 Problem solved. ||||| Are you smarter than a Singaporean high school student? Here’s one way to find out. 
 
 A math problem intended for sophomores and juniors in Singapore has become the obsession of some portion of the Internet over the past few days. The students were asked to answer a seemingly simple question: “When is Cheryl’s birthday?” 
 
 To figure it out, you’re provided with some vague clues. Cheryl separately gives two new friends some details about when she was born, including a list of 10 possible birth dates. She also tells one of the friends, Albert, the month of her birthday, then tells the other friend, Bernard, the day of her birthday. 
 
 As a final clue, there’s a conversation between Albert and Bernard, in which they each talk about what they know. 
 
 Now go solve the riddle! 
 
 Stumped? You’re not alone. 
 
 The question first appeared on April 8, as part of the Singapore and Asian Schools Math Olympiads contest. It was posted online Friday by a Singaporean television presenter and quickly went viral — perhaps because the problem was initially misidentified as one intended for 10- and 11-year-olds. 
 
 As the problem spread far and wide, it became a bit of a joke. Truthfully, we blame no one for choosing to laugh instead of crying out of frustration. 
 
 Albert and Bernard later went out and over drinks, compared notes and decided Cheryl and her frigging birthday wasn't worth their time. — mrbrown (@mrbrown) April 14, 2015 
 
 So when is Cheryl's birthday? Just check her Facebook. — Songhua (@songboh) April 12, 2015 
 
 There was so much attention focused on this problem that the Singapore and Asian Schools Math Olympiads organizers released a statement clarifying who the problem was intended for, so that “Singapore parents will not start to worry so much.” 
 
 [The inside story of the ‘white dress, blue dress’ drama that divided a planet] 
 
 The question is actually from a test given to students who are sophomores or juniors in high school — not middle school kids. And it comes deep into the exam and is one of the more difficult problems that students encounter. 
 
 “Being Question 24 out of 25 questions, this is a difficult question meant to sift out the better students,” Math Olympiads organizers wrote in a statement. “SASMO contests target the top 40% of the student population and the standards of most questions are just high enough to stretch the students.” 
 
 So yes, breathe a sigh of relief. And then take out a pencil and paper. 
 
 [How a middle school math teacher became Jordan Spieth’s caddie] 
 
 By this point there are more than a few answers out there, including the official one from SASMO. 
 
 And here is a video tutorial that can walk you through the solution:
– Never mind the color of that dress: When is Cheryl's birthday? The latest viral puzzler to stump the Internet started out as a question for students in Singapore and spread around the world after it was posted here, reports the Washington Post. Students were asked to determine the birthday of a girl called Cheryl, who had given new friends Albert and Bernard a list of 10 possible dates and told one boy the month and the other the day. The puzzler was initially identified as one for 10- or 11-year-old students, causing mild alarm for Singaporean parents, but it turned out to be a question for high school sophomores and juniors at the Singapore and Asian Schools Math Olympiads. "It's a really difficult question for younger kids, so that's why people were so shocked at first ... but now that people know it's for older students, they just think it's quirky," the Singapore TV presenter who first posted it tells the BBC. The math competition posted the answer here. At the New York Times, Kenneth Chang provides a detailed explanation while wondering, "Why is Cheryl so coy about revealing the month and day, but not year, of her birthday? What else is Cheryl trying to hide?" (A Tacoma man developed incredible mathematical abilities after being beaten up outside a karaoke bar.)