'Cheryl's Birthday' Math Problem Puzzles World

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.)