Monday, August 24, 2009

I Know You Can't Know That

A little puzzle I was offered today, which might perhaps be interesting. I will give what I think is the solution at the end of the week. A teacher says to their pupils, at some point this week I will give you a test, which you will not know is a test until I tell you afterwards. Given that if the test hasn't taken place in the last couple of minutes of Friday, the students will seemingly rightly think that it will take place then, and likewise for the couple of minutes before then, and so on, until the teacher is apparently compelled to say that the test has already been taken, can what the teacher says be true?