Combinatorics
Source: 1995 Belarus IMO TST Day 2 P 2
November 28, 2015
geometry3D geometryparallelepiped
Problem Statement
There is a room having a form of right-angled parallelepiped. Four maps of the same scale are hung (generally, on different levels over the floor) on four walls of the room, so that sides of the maps are parallel to sides of the wall. It is known that the four points corresponding to each of Stockholm, Moscow, and Istanbul are coplanar. Prove that the four points coresponding to Hong Kong are coplanar as well.