Per and Kari each have n pieces of paper, they write numbers 1 to 2n
Source: Norwegian Mathematical Olympiad 1996 - Abel Competition p3
February 11, 2020
combinatoricscombinatorics solved
Problem Statement
Per and Kari each have pieces of paper. They both write down the numbers from to in an arbitrary order, one number on each side. Afterwards, they place the pieces of paper on a table showing one side. Prove that they can always place them so that all the numbers from to are visible at once.