streets avenues and crescents in a city (2016 Auckland MO S5)
Source:
November 13, 2021
combinatorics
Problem Statement
In a city at every square exactly three roads meet, one is called street, one is an avenue, and one is a crescent. Most roads connect squares but three roads go outside of the city. Prove that among the roads going out of the city one is a street, one is an avenue and one is a crescent.