Answer: |
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Four
colors. |
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Complete
Solution: |
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The least number
of colors needed for this map is four. One
possible solution, shown in Figure 1 at
right, uses the colors red, green, yellow and blue. |
 fig.
1
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It is not possible
to use fewer than four colors. If a state is
surrounded by an even number of states, alternate two
colors as you move around the states. The surrounded state
will require a third color, as in Figure 2
at right. |
 fig.
2
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If
a state is surrounded by an odd number of states,
the surrounding states require three colors, and the surrounded
state requires the fourth color. See Figure 3. |
fig.3
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