ISL 2017 N2
Let be a prime number. Eduardo and Fernando play the following game making moves alternately: in each move, the current player chooses an index in the set that was not chosen before by either of the two players and then chooses an element of the set . Eduardo has the first move. The game ends after all the indices have been chosen. Then the following number is computed: The goal of Eduardo is to make the number divisible by , and the goal of Fernando is to prevent this. Prove that Eduardo has a winning strategy. (Morocco)
Dataset text NuminaMath olympiads. Quoted with source.
Official text: IMO 2017 Shortlist booklet, page 12.
Solutions
Official solution Solution 1 by the IMO Problem Selection Committee
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