Skiing competition with one change of leader
Source: Poland Math Olympiad 1995 Round 1 #11
July 18, 2023
probability
Problem Statement
In a skiing jump competition contestants take part. They jump with the previously established order. Each of them jumps once. We assume that the obtained results are different and the orders of the contestants after the competition are equally likely. In each moment of the competition by a leader we call a person who is scored the best at this moment. Denote by the probability that during the whole competition there was exactly one change of the leader. Prove that .