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Weekly Problem 41 - 2007
The Queen of Spades always lies for the whole day or tells the truth for the whole day. Which of these statements can she never say?


Stage: 4 Challenge Level: Challenge Level:2 Challenge Level:2

We are given a regular icosahedron having three red vertices. Show that it has a vertex that has at least two red neighbours.

If you're stuck, try this proof sorting activity.


This problem was taken from the Hungarian magazine KoMaL. There are many other challenging problems in English on the KoMal website.