test quiz

[kopend]

a teacher tells her class they will have a test next week, she will only tell them on the morning of the quiz that the test will be that afternoon.how can this not be a surprise.

i dont know the answer but i know it cant be on a friday and you have to work it back from there

[gen2]

This is an old paradox and is usually told about a prisoner who is going to be executed.  In your version, the logic goes like this:

If the teacher left it to Friday, then since that is the last possible day, it would not be a surprise because they could have deduced it by noon the previous day.  Therefore the surprise test cannot be Friday.

Now since Friday is ruled out, Thursday becomes the last possible day for the test, but if the test wasn't announced by noon on Wednesday, they could deduce that it would be on Thursday (remember it cannot be Friday) and again it wouldn't be a surprise.  Therefore the surprise test cannot be Thursday or Friday.

Now since Thursday and Friday are ruled out, Wednesday becomes the last possible day for the test, but if the test wasn't announced by noon on Tuesday, they could deduce that it would be on Wednesday(remember it cannot be Thursday or Friday) and again it wouldn't be a surprise.  Therefore the surprise test cannot be Wednesday, Thursday or Friday.

. . . and so on for the rest of the week.  The class have deduced that the test could not be a surprise on any of the days of the week.  Imagine their surprise then when the teacher announces on Tuesday morning that the test will be that afternoon!  Hence the paradox - will it be a surprise or won't it?