minimal number of places where Alice has spent the New Year
Source: Tournament of Towns, Senior Ο-Level Paper, Spring 2020 , p2
June 4, 2020
combinatorics
Problem Statement
Alice asserts that after her recent visit to Addis-Ababa she now has spent the New Year inside every possible hemisphere of Earth except one. What is the minimal number of places where Alice has spent the New Year?Note: we consider places of spending the New Year to be points on the sphere. A point on the border of a hemisphere does not lie inside the hemisphere.Ilya Dumansky, Roman Krutovsky