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Sylvia simplified the expressions on the Expression Comparison Mat shown below. Some of her work is shown. Are all of her moves legal? Explain.

Expression Comparison Mat Which is greater? Upper Left: 2 positive x tiles, 1 negative unit tile. Upper Right: 2 positive x tiles, & 1 positive unit tile. Lower Left & right each has 1 positive unit tile. Movement. Step 1. Remove 1 negative unit tile and 1 positive unit tile from the left. Step 2. Remove 2 positive x tiles from both the upper left and right. Step 3. Move unit tile from lower right to upper right. flipping it to negative. Then remove them.

Go through your list of legal moves and check each move made by Sylvia.

Removing the same amount from both sides is a legal move.

Flipping tiles from the subtraction region to the addition region and changing it from positive to negative is a legal move.

Removing zero pairs is a legal move.

Removing a positive tile from the (−) region and a negative tile from the (+) region is not a legal move, because they do not make a zero pair.