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'Cheryl's Birthday' Problem Gets the Internet Talking About Math

It's been a tough year for parents trying to keep up with their kids in math.

Last March, a North Carolina father tried to help his son with a word problem and ended up writing a note to the teacher saying that, despite having a degree in engineering, he couldn't figure it out. Both the note and problem went viral.

Parents have also been taking to social media to complain about the "new" methods their children are learning for basic computation under the Common Core State Standards

Then last week, this high school problem from Singapore made the rounds on the Internet:

This question causes a debate with my wife .... and its a Sec 3 question. #trickquestion#cherylsbirthday

Posted by Kennethjianwen on Friday, April 10, 2015

The Singapore television host who posted the problem wrote that it was for students in the equivalent of 5th grade. That made some parents panic.

It turns out that the problem actually came from a math competition known as the Singapore and Asian School Math Olympiad, which is aimed at the top 40 percent of high school students. 

I won't spoil the fun and attempt to explain the answer—but you can find excellent explanations of how to figure it out here, here, and here. (Several sites have reworded the problem as well for clarity.)

Since the problem was posted, much has been made of the fact that Singapore scores well above the United States on the Program for International Student Assessment, a global assessment of 15-year-olds. In 2012, U.S. students scored an average of 481 in math, while Singapore's students scored an average of 573. Twenty-nine nations outperformed the U.S. to a statistically significant degree, and Singapore was outscored by only one—Shanghai-China.

But there are always caveats with PISA scores, so perhaps a better comparison is this: What percentage of math olympians in Singapore got the correct answer to the problem? And what percentage of the top 40 percent of U.S. high school students could do the same? 

In any case, it's been fun to see the Internet struggle with and endlessly debate a logic problem. There's been so much of this that the Math Olympiad group posted an entire explanation of why one particular answer that many people online have argued for is wrong. 

Many sites have also posted similar problems, since this one generated so much interest. You can find other bemusing problems here and here

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