MathDB
2024 COMC B4

Source:

November 4, 2024
Comc

Problem Statement

Initially, the integer 8080 is written on a blackboard. At each step, the integer xx on the blackboard is replaced with an integer chosen uniformly at random among [0,x−1], unless x=0x=0 , in which case it is replaced by an integer chosen uniformly at random among [0,2024]. Let P(a,b)P(a,b) be the probability that after aa steps, the integer on the board is bb. Determine limxP(a,80)P(a,2024)\lim_{x\to\infty}\frac{P(a,80)}{P(a,2024)} (that is, the value that the function P(a,80)P(a,2024)\frac{P(a,80)}{P(a,2024)} approaches as aa goes to infinity).