A rectangle has positive integer side lengths and an area of 24. What perimeter of the rectangle cannot be?
Solution
Since the rectangle has positive integer side lengths and an area of 24, its length and width must be a positive divisor pair of 24. Therefore, the length and width must be 24 and 1, or 12 and 2, or 8 and 3, or 6 and 4. Since the perimeter of a rectangle equals 2 times the sum of the length and width, the possible perimeters are , , , . These all appear as choices, which means that the perimeter of the rectangle cannot be 36.
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