MathDB

6

Part of 2013 Bangladesh Mathematical Olympiad

Problems(1)

Road to go $n$ cities.

Source:

2/9/2017
There are nn cities in a country. Between any two cities there is at most one road. Suppose that the total number of roads is n.n. Prove that there is a city such that starting from there it is possible to come back to it without ever travelling the same road twice.
combinatorics