MathDB
Wandering Token

Source: 2014 AIME I Problem 11

March 14, 2014
analytic geometryprobabilitysymmetryAMCAIMErotationgeometry

Problem Statement

A token starts at the point (0,0)(0,0) of an xyxy-coordinate grid and them makes a sequence of six moves. Each move is 11 unit in a direction parallel to one of the coordinate axes. Each move is selected randomly from the four possible directions and independently of the other moves. The probability the token ends at a point on the graph of y=x|y|=|x| is mn\tfrac{m}{n}, where mm and nn are relatively prime positive integers. Find m+nm+n.