A professor tells his class that he will give them a surprise examination sometime next week.

For our purposes, an examination is considered a "surprise" if on that day, the class is not 100% sure that they will get an examination. (If they only suspect it, the examination can still be a surprise.)

Having given the class this warning, is it still possible for the professor to give them a surprise examination next week? (Assume that he will not give them an exam if it will not be a surprise.)

(In reply to not true by srikumar)

Exactly what I thought. The only way for this to be a paradox is for the teacher to conduct the test on Friday, since no one expects him to give it on that day. As for the other days, he can conduct the test and, for at least one student, it will be a surprise.

The recursive process used to eliminate the other days of the week is not mutually exclusive; in other words, we eliminated friday DUE TO THE FACT that the teacher didnīt conduct the test on the other days. But we canīt eliminate the other days using the same process.

:)

Posted by Bruno on 2003-09-30 12:23:22