Feature

Cheryl’s birthday: Part 2?

By Jane Ng
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Photos: Li Haolun

It does not compute and may not sound logical, but Dr Joseph Yeo Boon Wooi of “Cheryl’s birthday” fame did not do well in his first mathematics test in junior college.

National Institute of Education lecturer Dr Yeo, who is in his 40s, was the one who came up with the version of the logic question that went viral across the world.

But the media-shy lecturer who trains mathematics teachers is uncomfortable with his newfound recognition and says he prefers to focus on encouraging students: “The most important thing when tripping up on a test is not to be discouraged, but to examine what went wrong and to strategise how you can improve.”

Dr Yeo is in the panel that sets questions for the Singapore and Asian Schools Math Olympiads. Among the questions he put together for this year’s competition was the “Cheryl’s birthday” poser. His version had Secondary 3 students guess the date of Cheryl’s birthday using clues provided to her friends, Albert and Bernard.

It does not matter that he is not the original creator of the problem, because it is his version that went viral online. The problem was covered in The Guardian and The New York Times, and now has its own Wikipedia entry.

Surprised by this outcome, Dr Yeo says: “I just modified an existing version by changing various things, including the storyline. I need to reiterate that credit should go to the original creator, not me.”

The “Cheryl’s birthday” puzzle that went viral. Have you solved it yet?

Dr Yeo, who has enjoyed solving mathematics and logic problems since he was young, decided early on to be a mathematics teacher and applied for a teaching scholarship.

Teaching students of varying maths abilities at both Yuan Ching Secondary School and Anglo-Chinese School (Independent) convinced him about the need for effective teaching strategies for different students. Eager to further his interest in maths education, he went on to do his doctorate. He has been lecturing at the National Institute of Education at NTU for more than 10 years.

One of his areas of expertise is to teach trainee teachers how to motivate and engage their charges by using a variety of resources. These include songs and videos, comics, newspaper articles, brainteasers, logic games, interesting stories of famous mathematicians, and real life examples and applications.

The genial academic may have won teaching awards for his methods, but he says: “As a mathematics teacher, you don’t teach maths. You teach students.”

“You cannot save all the starfish, but it makes a difference to the one you save.”
“If you teach mathematics, you could be just delivering a lesson, and that’s it. Even if you want your students to do well in the subject, it is still about their academic results for your subject. But if you teach students, you care about their entire well-being,” adds Dr Yeo, who has a supportive wife and two children.

So instead of focusing on only a student’s mathematics results, a teacher should also be looking out for the student’s performance in other subjects. Likewise, if a student has problems outside of school and cannot focus in class, a teacher should be more concerned about the student’s problems rather than his school work, says Dr Yeo.

He tells his students the well-known starfish story by Loren Eiseley – you cannot save all the starfish, but it makes a difference to the one you save. So it makes his day when he gets emails from former trainee teachers to say that they are still teaching students, “saving” them, one at a time.

When “Cheryl’s birthday” became a celebrated success overnight, it came with a surprise gift for Dr Yeo: “I have a friend who went to the United States to study when we were in junior college. In those days, we wrote letters. There was no email. Then we lost contact. I have been wondering how to find him. Now he found me. Thank you, Cheryl.”

Now figure out Cheryl’s age...
If you’ve been following the buzz on “Cheryl’s birthday”, you should know that her birthday is 16 July. In the question, Cheryl gives her new friends, Albert and Bernard, 10 possible dates when they enquire about her birthday, before separately giving each of them further clues.

The cryptic puzzle and its solution can be found online at numerous sites like The Straits Times, The New York Times, BBC and BuzzFeed.

Raring to test your reasoning skills again? Try part two of the puzzle that Dr Yeo has put together for HEY! readers:

Albert and Bernard now want to know how old Cheryl is.
Cheryl: I have two younger brothers. The product of all our ages (i.e. my age and the ages of my two brothers) is 144, assuming that we use whole numbers for our ages.
Albert: We still don’t know your age. What other hints can you give us?
Cheryl: The sum of all our ages is the bus number of this bus that we are on.
Bernard: Of course we know the bus number, but we still don’t know your age.
Cheryl: Oh, I forgot to tell you that my brothers have the same age.
Albert and Bernard: Oh, now we know your age.

Click here for the solution.