This problem originally appeared in 1978, as a challenge question. As stated then,1
Four birds land at random positions on a finite length of wire. Upon landing, each bird looks at its nearest neighbor.
a. What is the probability that a bird picked at random is looking at another bird that is looking at it?
b. What is the probability if there are n birds, with n > 4?
The solution appeared the next year.2 (I have converted the birds into cars and the wire into a car lot to, I hope, make the problem more “relevant”.) ...