Chapter 9.2, Problem 29E

Figure 9.7 on page $673$ shows a map of the BART (Bay Area Rapid Transit) system.

On that map, different rapid transit lines are colored differently. For example, the rapid transit line between Millbrae and Pittsburg/Bay Point is colored yellow.

(a) Draw a graph of this. If two adjacent stations have three different lines connecting them, then those stations vertices should have three different edges connecting them.

(b) Is there a BART ride if the drive’s starting point must be the same as its stopping point? If your answer is “yes,” describe the drive. If your answer is “no,” explain why. Then Eulerize the graph if possible.

(c) Is there a BART ride if the drive’s starting point must be different from its stopping point? If your answer is “yes,” describe the drive. If your answer is “no,” explain why. Then Eulerize the graph if possible.

(d) Explain why the existence of a BART ride would be important to BART police, who regularly ride BART to provide security.

(e) Which type of BART ride would be more useful to BART police: the type described in part (b) or the type described in part (c)?why ?