The Math Question That Went Viral

One word problem from a Singaporean school exam briefly became the talk of the Internet last weekend.

Mario Anzuoni/Reuters

It didn't rise quite to the level of "The Dress"—the recent quandary that resulted in accusations of color-blindness across the Internet—but it still gave the education world its own viral moment over the weekend. A viral math question, in fact.

Last Friday, the Hello Singapore TV host Kenneth Kong posted a mathematical riddle to his Facebook page with the caption: "This question causes a debate with my wife .... and its a P5 question." The puzzle went viral across the country, with people ranging from perplexed adults to eager teenagers grappling with the simple question: "So when is Cheryl's birthday?"

Kenneth Kong/Facebook

The hysteria wasn't limited to Singapore. The question immediately made the rounds on Twitter—along with the hashtag #cherylsbirthday—and Reddit. It even made its way to the Australian Federation of International Students' Facebook page.

Without giving away the answer, here's a good starting point:

Albert knows the month, Bernard knows the number.
Albert knows that Bernard doesn't know.
Look at how many times each date appears.
Figure out which month Albert was told, and begin the elimination process.

The riddle worried some parents. "P5," known as "Primary 5" in the Singaporean education system, is the equivalent of 5th grade in the United States. Despite Singapore's internationally revered math proficiency, many parents were concerned that the question was far too advanced for their kids.

This prompted an investigation of sorts by, a Singaporean news outlet. The organization obtained official confirmation (spoiler: the answer is included as well) from the executive director of the Singapore and Asian Schools Math Olympiad. According to the director, Henry Ong, the question was in fact for older "Secondary 3" students, or the equivalent of ninth grade here in the U.S. Ong also admitted that it was "a difficult question meant to sift out the better students."

Logical puzzles like this are common in Singapore. The country's math curriculum, which has a strong focus on logic-based problem solving, has been so successful that it's been adopted around the world, including in the U.S.

According to the latest report from the Program for International Student Assessment (PISA)—an exam designed to measure the math, reading, and science proficiency of 15-year-olds globally—Singapore's math competency essentially outshines that of the rest of the world:

Singapore scores highest in the PISA 2012 assessment of problem solving, with 562 points on the PISA proficiency scale. Only Korea has a similarly high score.

Singapore also has the highest number of top-performing students in problem solving: 29 percent of students reach proficiency Level 5 or 6 (the OECD average is 11 percent).

Performance in Problem Solving in Singapore

So what makes Singapore so good at a subject with which America's students have routinely struggled? Singapore's math instruction focuses heavily on mastery over rote memorization. Math students on the small island nation perform well because they understand the material deeply—not because they are studying for a specific test. Thus, they react well when "curveballs" are thrown at them in the form of confusing math questions.

Furthermore, the instruction of "Singapore Math"—as it's dubbed in the U.S. —uses a "layered" approach aimed at facilitating comprehension. Students digest the subject in stages, from the concrete to the pictorial and eventually to the abstract. This leads to conceptual understanding rather than numerical regurgitation: It's not just about getting the correct answer, but also about explaining one's thought processes.

U.S. students have made strides in math proficiency in recent years, but they still lag behind many of their peers internationally, falling at the middle of the pack in global rankings. In the same PISA report the U.S. placed 35th out of 64 countries in math.  

And even though the "Cheryl's Birthday" question may be atypical of the average Singaporean classroom, perhaps it's still worth asking: Are you smarter than a (Singaporean) 10th-grader?