MathDB
2018 Combinatorics #6

Source:

February 12, 2018

Problem Statement

Sarah stands at (0,0)(0,0) and Rachel stands at (6,8)(6,8) in the Euclidena plane. Sarah can only move 11 unit in the positive xx or yy direction, and Rachel can only move 11 unit in the negative xx or yy direction. Each second, Sarah and Rachel see each other, independently pick a direction to move, and move to their new position. Sarah catches Rachel if Sarah and Rachel are every at the same point. Rachel wins if she is able to get (0,0)(0,0) without being caught; otherwise, Sarah wins. Given that both of them play optimally to maximize their probability of winning, what is the probability that Rachel wins?