Singapore’s mind-bending logical riddles are so last month. Enter: Vietnam, the latest country to be swept up in what could easily be known as “the viral-math epidemic of 2015.”
This one might even trump its Singaporean predecessor, which became a global legend earlier this year. That quandary, for those who aren’t familiar with it, asked fifth-graders to figure out the birthday of a certain “Cheryl,” who gave two of her friends—“Albert” and “Bernard”—a list of 10 possible dates. She then privately told Albert the month, and Bernard the day. (“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 now know. Albert: Then I also know when Cheryl’s birthday is.”)
The question: So when is Cheryl’s birthday, really? The befuddlement that ensued, first among angry parents and then among Internet users around the world, prompted a #cherylsbirthday Twitter trend. Many wondered whether it even had to do with math.
The Vietnam question, however, is based on simple arithmetic; it has a Sudoku-esque feel. Unlike the Singaporean conundrum (which an investigation later found was actually meant for ninth-graders and had been designed to “sift out the better students”), this one isn’t aimed at deliberately confusing kids. It’s just really tough. According to reports, the question in question is designed for third-graders (i.e., 8-year-olds) in the town of Bac Loc in the Vietnamese highlands—students who, as one teacher told a local news outlet, tend to have lower proficiency levels than their peers in more developed parts of the country. (You’ll find the actual question, and a link to its solution, further down.)