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A city has four urban areas, A, B, C and D, which are distributed as shown in figure 1- 1-3. Now five different colors are drawn on the map of the city, and adjacent areas are required.
180

There are five different ways to draw a line graph, then B, and there are four different ways to draw one of the remaining four colors. Similarly, there are three different ways to draw C. Finally, there are three different ways to draw D. As long as it is different from B and C, according to the principle of multiplication, there are 5×4×3×3= 180 different ways to draw.