Maps.

Wiles county contains eight townships as shown on the map. If there are four colors available, in how many ways can the map be colored so that each township is colored with one color and no two townships that share a border are colored with same color?

603 578 700 576 600

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1 solution

Hana Wehbi
Oct 10, 2017

Label the townships as shown. There are four choices for colors for township A A , and three choices for colors for township B . B.

If townships C C and D D have the same color, then there are two choices for the color of C C and D D , and there are two choices for colors for each of the remaining townships E , F , G and H E, F, G \text{ and } H .

If townships C and D C \text{ and } D have different colors, then there are two choices for the color of C C and one choice for a color D D .

Since B , C and D B,C \text{ and } D will have different colors, there is only one choice of color for township E E . Then there are two choices for colors for each of the remaining townships F , G , and H F, G, \text{ and } H .

Thus, the total number of ways to color the 8 8 townships is: ( 4 × 3 × 2 × 2 × 2 × 2 × 2 ) + ( 4 × 3 × 2 × 1 × 2 × 2 × 2 ) = 576 . (4\times3\times2\times2\times2\times2\times2) + (4\times3\times2\times1\times2\times2\times2) = \boxed{576}.

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