Maths Tutoring:~ Cheryl's birthday puzzle


It's a maths question, but not as we know it.

The question below caused some consternation when it started to circulate in the media. It was mistakenly suggested that it was set for 10 year olds in Singapore. It now transpires that it was set before the brightest 14 to 15 year olds in that country.

Initially, when I looked at this question I stared at it with growing frustration. Is it a real question? It isn't like one we commonly see in maths exams set for schools. Is it a trick question? Finally, I go angry with myself. Why can't I do this? Am I stupid? I have listed the thoughts my mind subjected me to, to illustrate that even more confident maths practitioners suffer doubts, fears and anger. But as you get more confident you become more stubborn, or perhaps becoming more stubborn is a quality needed to become more confident at maths. Anyway, here is the question:

Singapore and Asian Schools Math Olympiad (SASMO) 2015 Contests Q24

24. Albert and Bernard have just become friends with Cheryl, and they want to know when her birthday is. Cheryl gives them a list of 10 possible dates:

May 15 May 16 May 19
June 17 June 18  
July 14 July 16  
August 14 August 15 August 17

Cheryl then tells Albert and Bernard separately the month and the day of her birthday respectively.

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

Bernard: At first I don't know when Cheryl's birthday is, but I know now.

Albert: Then also know when Cheryl's birthday is.

So when is Cheryl's birthday?

To view the Word file showing a way to step through the problem click here.




Pumpkin Logo