Tuesday, April 14, 2015

Cheryl's Birthday

People are talking on the internet about a problem given at a math contest in Singapore, the problem even has a name now, "Cheryl's Birthday". Some were shocked that such a problem was given to 11 years old students (in fact it was given to 15 years old children), but actually there is nothing that would prevent a 4th or 5th grade student to solve it. You need to know only basic logic operations, nothing more, so it is reasonable for an 11 years old child who is good at math to solve such a problem. |Actually when I was in 4th grade I started attending a math circle at  my school and we were doing exactly this kind of problems. I remember even today how happy I was when I solved one of the first of those logic problems and of course I remember that problem too: There was a kingdom having capital punishment. Before execution each convicted person was allowed to appear in front of the king and say a statement. If the statement was false he would be beheaded and if the statement was true he would be hanged. How can a man escape execution in these circumstances?

Many years after I was attending a job interview in Bucharest. It was in those years when people found out that Google and Microsoft gave logic problems at interviews and the fashion spread to other companies. They gave me one problem which I solved and then they gave me a second one which I knew from the math circle. They asked me where do I know it and when I told them that I know it from the 4th grade and I used to solve this kind of problems every week they decided to skip that part of the interview :)

Now don't imagine that I attended some privileged private school. I was raised in Mangalia, a small town in communist Romania, and I went to the nearest school from my house which was still half an hour walk. It was the dedication of some passionate math teachers (Mr. Dinu, Craciunescu and Henny) who were willing to spend their week-ends teaching some extra hours of math for free to some little kids like me and many others. You know, I have to thank them once again here for their effort.

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