A teacher decides to give a pop quiz one day but all of her students refuse to take the quiz thinking that the teacher will call off the quiz. She can give only one of these students a detention for skipping the quiz. All of the students know each other’s names and if a student knows he/she is getting a detention they take the quiz.
How can she threaten her students with the single detention so they all take the quiz?
Answer
She tells them that she will give the student who skips the quiz whose name comes first alphabetically a detention.
This student won’t skip because they know they are getting a detention if they do. The next person alphabetically will then know that they will get a detention so they won’t skip either, and so on.