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Printimc
geometry intermediate
Problem
A rectangle with positive integer side lengths in has area and perimeter . Which of the following numbers cannot equal ?
(A)
(B)
(C)
(D)
Solution
Let the rectangle's length be and its width be . Its area is and the perimeter is . Then . Factoring, we have . The only one of the answer choices that cannot be expressed in this form is , as is twice a prime. There would then be no way to express as , keeping and as positive integers. Our answer is then . Note: The original problem only stated that and were positive integers, not the side lengths themselves. This rendered the problem unsolvable, and so the AMC awarded everyone 6 points on this problem. This wiki has the corrected version of the problem so that the 2015 AMC 10A test can be used for practice.
Final answer
B