MathDB
Turning coins on a table

Source: Saudi Arabia IMO TST Day III Problem 3

July 22, 2014
combinatorics unsolvedcombinatorics

Problem Statement

There are 20152015 coins on a table. For i=1,2,…,2015i = 1, 2, \dots , 2015 in succession, one must turn over exactly ii coins. Prove that it is always possible either to make all of the coins face up or to make all of the coins face down, but not both.
Back to ProblemsView on AoPS