Meet the mathematics lecturer behind 'Cheryl's birthday' puzzle

SINGAPORE - The man behind the "Cheryl's birthday" viral poser is a mathematics lecturer from the National Institute of Education (NIE).

Dr Joseph Yeo Boon Wooi, who is in his 40s, is part of the panel for the Singapore and Asian Schools Math Olympiads (SASMO), the largest math competition here.

He helps set the questions each year for student "mathletes".

This year's competition took place on April 8. The puzzle in question was leaked, and subsequently posted on Facebook on April 11 by local TV presenter Kenneth Kong, who initially mistook it for a Primary 5 question.

Dr Yeo, a recipient of the prestigious Nanyang Excellence in Teaching Award in 2013 and first author of the New Syllabus Mathematics used in secondary schools, said he first chanced upon a Facebook post discussing the birthday logic problem on April 12.

But it did not ring a bell until he saw the photo of the question.

It has since been featured on international media such as The New York Times, The Guardian and the BBC, and was a top-trending story on US site Buzzfeed. On April 16, "Cheryl" even got her own cartoon on The New Yorker.

The Straits Times caught up with the media-shy math whiz and persuaded him to answer some questions about himself and how he came up with the viral hit that has confounded the world.

Dr Yeo's birthday, coincidentally (or not), falls on July 16 - the answer to the puzzle.

How did you come up with the question "Cheryl's birthday"?

I set the question based on guidelines given by SASMO.

This question, like all other questions we set, was vetted and approved by a panel of local and overseas experts from the SASMO Partners' League, which organises SASMO contests in their own countries.

"Cheryl's birthday" is not a new logic problem. There are various versions which others have modified. I am not aware of the original source. I modified it by changing the names, dates and context or storyline.

What do you think of the buzz it has generated?

I first saw someone on Facebook talking about the Cheryl's birthday logic problem on Sunday (April 12). It didn't ring a bell.

Then I saw a photo of the question. I was like, "Heh! This looks familiar!" I still cannot believe that the question has gone viral.

Which aspect of math do you specialise in?

I am a lecturer with the National Institute of Education. I specialise in training student teachers how to teach secondary school maths.

How did you develop your interest in maths?

It just comes naturally to me. I enjoy solving maths and logic problems.

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