no of citizens wanted in X-wich, people and clubs related
Source: 1985 Swedish Mathematical Competition p6
March 28, 2021
combinatorics
Problem Statement
X-wich has a vibrant club-life. For every pair of inhabitants there is exactly one club to which they both belong. For every pair of clubs there is exactly one person who is a member of both. No club has fewer than members, and at least one club has members. How many people live in X-wich?