I’m still reading the book used by our department for “Topics in Finite Mathematics” and I found this interesting little snippet from the introduction to the section entitled “The Multiplication Principle”.
Here are some examples of counting problems that are unlike any we have seen up to this point, but that we should be able to answer after studying this section:
How many different Social Security numbers are possible?
How many different telephone numbers can be given the area code 870?
In how many ways can a president and a vice president be selected from among 12 people?
How many ways can the sum of eight be rolled on a pair of dice?
Here is my question for everyone: Which of the above four questions is the most different from the others? If you like, you might rephrase this as: Which of the above four questions doesn’t belong?
My answer differed from my wife’s answer and I think both are valid (but I won’t say what they were yet). I’d love to hear some other responses to this. If you happen to guess the same one I chose—for the same reason—then you win the grand prize for making me feel less alone in the universe. Sadly, the grand prize is merely reciprocity.