Baltic Way 2009 problem 20
Source:
December 30, 2009
analytic geometrygraphing linesslopecombinatorics proposedcombinatorics
Problem Statement
In the future city Baltic Way there are sixteen hospitals. Every night exactly four of them must be on duty for emergencies. Is it possible to arrange the schedule in such a way that after twenty nights every pair of hospitals have been on common duty exactly once?