MathDB
2018-2019 Fall OMO Problem 9

Source:

November 7, 2018

Problem Statement

Ann and Drew have purchased a mysterious slot machine; each time it is spun, it chooses a random positive integer such that kk is chosen with probability 2āˆ’k2^{-k} for every positive integer kk, and then it outputs kk tokens. Let NN be a fixed integer. Ann and Drew alternate turns spinning the machine, with Ann going first. Ann wins if she receives at least NN total tokens from the slot machine before Drew receives at least M=22018M=2^{2018} total tokens, and Drew wins if he receives MM tokens before Ann receives NN tokens. If each person has the same probability of winning, compute the remainder when NN is divided by 20182018.
Proposed by Brandon Wang