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Number theory Difficulty 4.5 AIME Prove it Estonia

Do there exist positive integers xx and yy such that
11x5+33y=13y5+31x+2024? 11x^5 + 33y = 13y^5 + 31x + 2024?

Solution

The given equation is equivalent to
(11x531x)+(33y13y5)=2024. (11x^5 - 31x) + (33y - 13y^5) = 2024.
The fifth power of any positive integer ends with the same digit as the number itself. Therefore, 11x511x^5 ends with the same digit as 11x11x, which in turn ends with the same digit as xx. Since 31x31x also ends with the same digit, the difference 11x531x11x^5 - 31x ends with zero. Similarly, the difference 33y13y533y - 13y^5 ends with zero. However, the sum of numbers ending in zero cannot end in four. Therefore, there are no integers that satisfy the given equation.

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