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MathNet 2024-part-04 — 168 problems (EN–VI) Question 126

Math Olympiad Vault · MathNet 2024-part-04 — 168 problems (EN–VI)

Question 126

Let $a$ and $b$ be two real numbers in the interval $(0, 1)$, so that $a$ is a rational number and
$$
\{na\} \ge \{nb\}, \text{ for every natural number } n.
$$

Prove that $a = b$. (We denote by $\{x\}$ the fractional part of the real number $x$.)