The document discusses using the fundamental counting principle to calculate the number of possible routes when traveling between multiple locations. It provides examples of calculating the number of routes from Southfork to Goodsoil by multiplying the number of road options at each location. It then applies the same principle to calculate the number of possible round trips between Southfork and Goodsoil without repeating roads. The fundamental counting principle states that if the first choice can be made in m ways and the second choice can be made in n ways, then there are m × n ways to select both.