The foor of a rectangular room is covered with equal numbers of red and blue square tiles. The room is x tiles wide and y tiles long. If only red tiles are placed around the edge of the room and all of them are used for the boundary, nd all possible values of x and y.
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Hint: given $x$ and $y$, can you make expressions for the number of border tiles and the number of non-border tiles? It often helps to draw a picture-it is easy to get the corners wrong.