(April 5, 2011 at 12:44 am)Tiberius Wrote: The professor for class Logic 315 says on Friday: "We're going to have a surprise quiz next week, but I'm not telling you what day... if you can figure out what day it will be on, I'll cancel the quiz."
. . .
On Tuesday, the professor gives the quiz, totally unexpected!
What's the flaw in the students' thinking?
I think the real problem why it cannot be solved mathematically is it is not a mathematics question.
By creating a logical edifice which rules out all the class days, they "know" the quiz cannot be held (as it would then not be a surprise).
Thus, any day it is held makes it a surprise, because all days have been logically ruled out. (It would be a bigger surprise if he held the quiz on Saturday.) The missing step in the students' logic is: they cannot know which day the professor has picked without asking him. All the logical shenanigans in the world trying to predict the day, or rule it out, still don't produce the real answer: what day -is- the prof going to hold his quiz? He asks them a different question than they try to solve. They try to solve what day he -cannot- hold it, when he -can- hold it any day (including Saturday).
James.
"Be ye not lost amongst Precept of Order." - Book of Uterus, 1:5, "Principia Discordia, or How I Found Goddess and What I Did to Her When I Found Her."
