A math teacher declared one Friday: "I will give you a drop quiz next week, and none of you will know which day it will be so prepare for every day!"
Now one of the brilliant students started reasoning on Saturday:
- We cannot have the drop quiz next Friday, otherwise we will all know for sure next Thursday (since we did not have the drop quiz yet) that the drop quiz will be on Friday and this will contradict the teacher statement!
- We cannot have the drop quiz next Thursday, otherwise we will know on Wednesday (since we did not have the drop quiz yet) that the teacher is left with no choice than to give us the drop quiz on Thursday, since he cannot give it on Friday (above)
- We cannot have it on Wednesday then for the same reason like above
- Nor on Tuesday
- Nor on Monday for that matter!!!
So in short, the teacher CANNOT maintain his promise!!
Still, the teacher gave them a drop quiz on Tuesday and nobody was prepared for it nor knew about it the day before!!
What's the error in this reasonning????
PS: I don't really have an answer but I'm really curious about your reasonning and maybe I can stop stressing about this!!
INTERSTING FACT: This situation actually took place during World War II when a radio station (british I think) announced that they will have a very high profile guest on one of their show during a certain month (April I think). But due to the sensitivity of the situation, they cannot annouce the actual date of the interview for security reasons. They cannot have people knowing the date before the interview. So a Mathematician send them a telegram saying: "This cannot be done STOP"
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roolstar
Well this always bugged me!
A math teacher declared one Friday: "I will give you a drop quiz next week, and none of you will know which day it will be so prepare for every day!"
Now one of the brilliant students started reasoning on Saturday:
- We cannot have the drop quiz next Friday, otherwise we will all know for sure next Thursday (since we did not have the drop quiz yet) that the drop quiz will be on Friday and this will contradict the teacher statement!
- We cannot have the drop quiz next Thursday, otherwise we will know on Wednesday (since we did not have the drop quiz yet) that the teacher is left with no choice than to give us the drop quiz on Thursday, since he cannot give it on Friday (above)
- We cannot have it on Wednesday then for the same reason like above
- Nor on Tuesday
- Nor on Monday for that matter!!!
So in short, the teacher CANNOT maintain his promise!!
Still, the teacher gave them a drop quiz on Tuesday and nobody was prepared for it nor knew about it the day before!!
What's the error in this reasonning????
PS: I don't really have an answer but I'm really curious about your reasonning and maybe I can stop stressing about this!!
INTERSTING FACT: This situation actually took place during World War II when a radio station (british I think) announced that they will have a very high profile guest on one of their show during a certain month (April I think). But due to the sensitivity of the situation, they cannot annouce the actual date of the interview for security reasons. They cannot have people knowing the date before the interview. So a Mathematician send them a telegram saying: "This cannot be done STOP"
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