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Problem 271

Number theory Difficulty 2.3 Multiple choice CEMC Cayley · Canada · 2022

A rectangle has positive integer side lengths and an area of 24.
The perimeter of the rectangle cannot be

Pick one

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Official 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

2(24+1)=502(24 + 1) = 50
2(12+2)=282(12+2) = 28
2(8+3)=222(8+3) = 22
2(6+4)=202(6+4) = 20

These all appear as choices, which means that the perimeter of the
rectangle cannot be 36, which is (E).

Source: CEMC, University of Waterloo, licensed CC-BY-NC-4.0. Statement reproduced verbatim; metadata (topic, difficulty, ordering) added by this project.