Mar 16, 2019
RAY: This was sent in by someone named Christopher from Atlanta, who writes:
My friend, Max says to me, “I just read that three of the first five presidents of the United States died, ready for this? On the Fourth of July. What do you think the odds of that happening are?” I reply, “No idea. But, I'll give you 10-to-one odds that I can name at least one of the three.”
Now I don't know anything about the first five presidents, he writes, except that their names are: Washington, Adams, Jefferson, Madison and Monroe. In that order.
So the question is: How am I justified in offering my friend 10-to-one odds when, guessing randomly, I have only a three-in-five chance?
RAY: What makes me so sure I can guess at least one of them on the first try? Well, if it hadn't been Monroe, the fifth guy, why would it say three of the first five? It would have said three of the first four. Monroe must be one of them.