MathDB

In the array of

13

squares shown below,

8

squares are colored red, and the remaining

5

squares are colored blue. If one of all possible such colorings is chosen at random, the probability that the chosen colored array appears the same when rotated

90^{\circ}

around the central square is

\tfrac{1}{n}

, where

n

is a positive integer. Find

n

. [asy] draw((0,0)--(1,0)--(1,1)--(0,1)--(0,0)); draw((2,0)--(2,2)--(3,2)--(3,0)--(3,1)--(2,1)--(4,1)--(4,0)--(2,0)); draw((1,2)--(1,4)--(0,4)--(0,2)--(0,3)--(1,3)--(-1,3)--(-1,2)--(1,2)); draw((-1,1)--(-3,1)--(-3,0)--(-1,0)--(-2,0)--(-2,1)--(-2,-1)--(-1,-1)--(-1,1)); draw((0,-1)--(0,-3)--(1,-3)--(1,-1)--(1,-2)--(0,-2)--(2,-2)--(2,-1)--(0,-1)); size(100); [/asy]

4

Problems(2)