MathDB
Romania NMO 2023 Grade 9 P4

Source: Romania National Olympiad 2023

April 14, 2023
floor functionnumber theory

Problem Statement

Let rr and ss be real numbers in the interval [1,)[1, \infty) such that for all positive integers aa and bb with ab    ara \mid b \implies \left\lfloor ar \right\rfloor divides bs\left\lfloor bs \right\rfloor.
a) Prove that sr\frac{s}{r} is a natural number.
b) Show that both rr and ss are natural numbers.
Here, x\lfloor x \rfloor denotes the greatest integer that is less than or equal to xx.