Depending on how literal-minded you are, you may want to alter the rules to read, "The object is to take the given grid and divide it into rectangles such that each contains exactly one numbered cell, which denotes its area." The difference is the addition of the comma. Without it, literal-minded (or smart-alecky) solvers could respond by creating rectangles with several numbers, exactly one of which denotes the rectangle's area, and several which do not denote its area.