Chapter 9, Lesson 2

Yesterday, David and Ruth learned that:
A network is a figure consisting of points (vertices) connected by lines (straight or curved, called arcs).
You can travel a network when it is possible to draw the figure without retracing any line or taking your pencil off the paper.

Today, David and Ruth learned that:
An even vertex has an even number of arcs meeting at the vertex.
An odd vertex has an odd number of arcs meeting at the vertex.
The degree of a vertex is the number of its arcs.

Identify each vertex as odd or even and tell its degree.