**Session Author: **Sam Vandervelde

The purpose for having students play the game of Criss-Cross is to motivate them to explain the underlying mathematical reason governing who wins or loses. This exploration should lead the students to form, test, and ultimately prove conjectures about how to win at Criss-Cross. The game illustrates a beautiful application of the Euler characteristic and gives them practice at elementary counting techniques as well.

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**Strategies:**

Try a smaller problem, Multiple representations**Topics:**

Mathematical Games, Combinatorics, Geometry**Styles:**

Game(s)**Mathematical Practices:**

MP3, MP4, MP7, MP8