MathDB
Point-set duality

Source: Romania JBMO TST 2024 Day 3 P4

July 31, 2024
combinatoricsset theory

Problem Statement

Let n3n\geqslant 3 be a positive integer and N={1,2,,n}N=\{1,2,\ldots,n\} and let k>0k>0 be a real number. Let's associate each non-empty of NN{} with a point in the plane, such that any two distinct subsets correspond to different points. If the absolute value of the difference between the arithmetic means of the elements of two distinct non-empty subsets of NN{} is at most kk{} we connect the points associated with these subsets with a segment. Determine the minimum value of kk{} such that the points associated with any two distinct non-empty subsets of NN{} are connected by a segment or a broken line.
Cristi Săvescu