IMO 2021 Shortlist A1

Let n be an integer, and let A be a subset of t0,1,2,3,...,5n u consisting of 4n 2 numbers. Prove that there exist a,b,c...

imomathematicsolympiadshortlistalgebra

IMO 2021 Shortlist A1

Category: Algebra

Problem

Let n be an integer, and let A be a subset of t0,1,2,3,...,5n u consisting of 4n 2 numbers. Prove that there exist a,b,c PA such that a ăb ăc and c 2a ą3b.