St. Petersburg MO 2017 Grade 11 P7
Source: St. Petersburg MO 2017 Grade 11 P7
May 3, 2018
combinatoricsnumber theory
Problem Statement
Given a convex polygon with vertices at lattice points on a plane containing origin . Let be the set of vectors going from to the vertices of the polygon, and be the set of vectors going from to the lattice points that lie inside or on the boundary of the polygon (thus, is contained in .) Two grasshoppers jump on the whole plane: each jump of the first grasshopper shift its position by a vector from the set , and the second by the set . Prove that there exists positive integer that the following statement is true: if both grasshoppers can jump from to some point and the second grasshopper needs jumps to do it, then the first grasshopper can use at most jumps to do so.