There are 16 hats: 4 red, 4 blue, 4 green, 4 yellow. Each of the 4 hats of a color are to be labeled a '+','-','x' or '÷' and all 4 arithmetic sign labels must be used exactly once per color. Thus a hat can be identified uniquely by it's color and symbol. Arrange the 16 hats in a 4x4 grid so that no two rows or columns have a repeating color or a repeating sign. Some hats are already labeled and placed in the grid.
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