MathDB
sum of at least 2 of every 3 elements of M lies on M , subset of R

Source: Switzerland - 2004 Swiss MO Final Round p2

December 26, 2022
combinatorics

Problem Statement

Let MM be a finite set of real numbers with the following property: From three different elements of MM can always be chosen two whose sum is located in MM. How many elements can MM have at most?