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If Rick is mad at Sue and Philip, Sue is mad at Terry, and Terry is mad at Rick, it might be hard to keep track of this information.

A model of the situation might look like this:

In this model, each circle represents a person and lines connect the people who might not want to sit at the same table.

These types of math models are called *graphs*. On graphs, circles
are called *vertexes* and lines that connect vertexes are called
*edges*.

It may be easier to color the map of South America as cheaply as possible if we first make a graph of the problem.

On your graph:

- What will the the vertexes represent?
- What will the edges represent?

Next: See a graph we made for South America

Back: Map Coloring