MathDB

9

Part of 2017 India PRMO

Problems(1)

2017 preRMO p9, 5 cities on island, every road no more than once to visit all

Source:

8/9/2019
There are five cities A,B,C,D,EA,B,C,D,E on a certain island. Each city is connected to every other city by road. In how many ways can a person starting from city AA come back to AA after visiting some cities without visiting a city more than once and without taking the same road more than once? (The order in which he visits the cities also matters: e.g., the routes A→B→C→AA \to B \to C \to A and A→C→B→AA\to C \to B \to A are different.)
combinatorics