Showing posts with label Cheryl's birthday. Show all posts
Showing posts with label Cheryl's birthday. Show all posts

Sunday, April 19, 2015

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

By Chew Hui Min, chuimin@sph.com.sg, The Straits Times, Published on 18 April 2015 2:36 PM


Dr Joseph Yeo Boon Wooi, a mathematics professor at the National Institute of Education, is the man behind the viral math
PHOTO: Dr Joseph Yeo Boon Wooi, a mathematics professor at the National Institute of Education, is the man behind the viral math poser "Cheryl's birthday".
PHOTO: COURTESY OF DR JOSEPH YEO BOON WOOI
https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjDiefMkSGeY0nkePZj3lKAPZDg939bdQMtTlPwADGOPgWSH10MPQOSeUygn_cPp010PWGPYI6NR4wbW0vQAeq5t8fGr4i7qCNGmyLqTs33uDEdhFlDVPzNgLdd6lcd-0_CrDHfJ9-Qk2g/s1600/dryeo1e.jpg
http://www.straitstimes.com/sites/straitstimes.com/files/20150418/dryeo1e.jpg
http://www.straitstimes.com/news/singapore/more-singapore-stories/story/meet-the-mathematics-professor-behind-cheryls-birthday-p


SINGAPORE - The man behind the "Cheryl's birthday" viral poser is a mathematics professor 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.


Here’s a supposedly P5 logic question going viral on Facebook that will melt your brain
PHOTO: Here’s a supposedly P5 logic question going viral on Facebook that will melt your brain
Posted by Jonathan Lim on 12 April 2015
https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjqMVK7Bogj40Lw3NDaYhGdBWdrsr_-QSh4A4NO9tfABNUZUacSvFXcE9YcCxu1fBJjZdgm6JN2B-zTKHsXGrGIvFa4Q1m7w3LEKt1XasAPSsnlclEv-jlQQolpkd17kBeNJFlJ-N8_fm0/s1600/trick-question.jpg
http://cdn.mothership.sg/wp-content/uploads/2015/04/trick-question.jpg
http://mothership.sg/2015/04/heres-a-supposedly-p5-logic-question-going-viral-on-facebook-that-will-melt-your-brain/


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.

By Chew Hui Min, chuimin@sph.com.sg, The Straits Times, Published on 18 April 2015 2:36 PM



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Next Level Cheryl Birthday Question


Next Level Cheryl Birthday Question
Albert, Bernard and David just became friends with Cheryl, and they want to know when her birthday is.

Cheryl gives them a Iist of 16 possible dates.

May 15    May 16    May 19   
Jun 11    Jun 18    Jun 20    Jun 22
Jul 15     Jul 16       
Aug 14    Aug 20    Aug 22   
Sep 14    Sep 16    Sep 17    Sep 20

Cheryl tells Albert and Bernard separately the month and the day of her birthday, respectively, She then chooses one particular date from the list and tells David, and makes it known to all that the chosen date has a different day and month from her birthday.

Albert: I don't know when Cheryl's birthday is, but l know that Bernard does not know too.

Bernard: I did not know when Cheryl's birthday is, and now I still don't.

Albert: I still don't know when Cheryl's birthday is. Having said that, I am sure David still does not know too.

David: I knew neither the day nor the month right before Albert said his last sentence¹, but after he did, now I know what month it is.

Bernard: I did not know when Cheryl's birthday is right before Albert said his last sentence, but after he did, I know when Cheryl's birthday is.

David: Then I also know when Cheryl's birthday is.

Albert: Now I know too.
 So when is Cheryl's birthday?(September 14) What date did Cheryl tell David?(June 20)
1. Last sentence refers to: "Having said that, I am sure David still does not know too."


Solution posted by FinitelyGenerated on 16 April 2015:
1) Albert: I don't know when Cheryl's birthday is, but l know that Bernard does not know too.
Eliminates May, June
Table1.jpg


2) Bernard: I did not know when Cheryl's birthday is, and now I still don't.
Eliminates 15, 17, 22 (Unique days)
Table2.jpg


3i) Albert: I still don't know when Cheryl's birthday is.
Eliminates July 16 (Unique Month).
Only the month August and September remains.
Table3i.jpg


3ii) Albert: Having said that, I am sure David still does not know too.
Eliminates August. (Albert knows the month. If David is given September 14 or 20 he would know Cheryl's birthday)
Only the month September remains.
Table3ii.jpg


4) David: I knew neither the day nor the month right before Albert said his last sentence¹, but after he did, now I know what month it is.
David was not given August or September as he could not deduce the month at first (step 3i). He was not told August 14 or 20.
Table4.jpg


5) Bernard: I did not know when Cheryl's birthday is right before Albert said his last sentence, but after he did, I know when Cheryl's birthday is.
Eliminates September 16 - because if it is 16 (unique before Albert said his last sentence), Bernard would have know before step 3ii).
Table5.jpg


6) David: Then I also know when Cheryl's birthday is.
David was able to eliminate one of 14, 20 so he must have been given June 20 as this is the only 14 or 20 not in August or September (Step 4).
Eliminate September 20.
Table6.jpg


7) Albert: Now I know too.
Only left September 14 as Cheryl's birthday.
Table7.jpg

Question submitted by iiyamabto on 16 April 2015
Solution posted by FinitelyGenerated on 16 April 2015



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Monday, April 13, 2015

P5 Maths question - When is Cheryl's birthday?




Here’s a supposedly P5 logic question going viral on Facebook that will melt your brain
PHOTO: Here’s a supposedly P5 logic question going viral on Facebook that will melt your brain
Posted by Jonathan Lim on 12 April 2015
https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjqMVK7Bogj40Lw3NDaYhGdBWdrsr_-QSh4A4NO9tfABNUZUacSvFXcE9YcCxu1fBJjZdgm6JN2B-zTKHsXGrGIvFa4Q1m7w3LEKt1XasAPSsnlclEv-jlQQolpkd17kBeNJFlJ-N8_fm0/s1600/trick-question.jpg
http://cdn.mothership.sg/wp-content/uploads/2015/04/trick-question.jpg
http://mothership.sg/2015/04/heres-a-supposedly-p5-logic-question-going-viral-on-facebook-that-will-melt-your-brain/


This logic was shared by a MediaCorp Channel 8 presenter Kenneth (江坚文 Jiāng jiān wén) [https://www.facebook.com/kennethjianwenz/photos/a.173663129479243.1073741827.167504136761809/385751114937109/?type=1&theater] on Facebook on Saturday 11 Apr.
 

In his Facebook post he said “This question causes a debate with my wife …. and its a P5 question. #trickquestion” [https://www.facebook.com/hashtag/trickquestion]
 
It is not known whether this is really a Primary 5 question or if it came from Singapore, but more importantly, can you solve the question?

Answer:
Table posted by Stephanie Ng Wan Jing
Texts (explanations) posted by Jun Cai
 

Here’s a supposedly P5 logic question going viral on Facebook that will melt your brain
PHOTO: P5 logic question
Posted by Jonathan Lim on 12 April 2015
https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjqMVK7Bogj40Lw3NDaYhGdBWdrsr_-QSh4A4NO9tfABNUZUacSvFXcE9YcCxu1fBJjZdgm6JN2B-zTKHsXGrGIvFa4Q1m7w3LEKt1XasAPSsnlclEv-jlQQolpkd17kBeNJFlJ-N8_fm0/s1600/trick-question.jpg 
http://cdn.mothership.sg/wp-content/uploads/2015/04/trick-question.jpg
http://mothership.sg/2015/04/heres-a-supposedly-p5-logic-question-going-viral-on-facebook-that-will-melt-your-brain/


July 16 is the only possible answer
1) Albert: I don't know when Cheryl's birthday is, but l know that Bernard does not know too.
A knows B confirm don't know the date, which means A wasn't told May or June because May and June both have an unique identifier (5/19 and 6/18) ie. If B was told 19 or 18 the entire Condition 1 is wrong.

Table-1.jpg

 
2) Bernard: At first I did not know when Cheryl's birthday is, but I know now.
We are left with July to August. B is now confident of his answer, so his Date must be unique, thus eliminating 7/14 and 8/14.

Table-3.jpg


3) Albert: Then I also know when Cheryl's birthday is.
A says he now knows the answer, because July is the only unique (There are two August dates, left)

Table-3.jpg


Posted by Jonathan Lim on 12 April 2015



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