MathDB
Find the probablity - ISL 1986

Source:

August 31, 2010
probabilitycombinatoricscountingIMO Shortlist

Problem Statement

A particle moves from (0,0)(0, 0) to (n,n)(n, n) directed by a fair coin. For each head it moves one step east and for each tail it moves one step north. At (n,y),y<n(n, y), y < n, it stays there if a head comes up and at (x,n),x<n(x, n), x < n, it stays there if a tail comes up. Letk k be a fixed positive integer. Find the probability that the particle needs exactly 2n+k2n+k tosses to reach (n,n).(n, n).
Back to ProblemsView on AoPS