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PAMO 2022 Problem 5 - Partition of set of natural numbers

Source: 2022 Pan-African Mathematics Olympiad Problem 5

June 26, 2022
combinatorics

Problem Statement

Let rr be a positive integer. Find the smallest positive integer mm satisfying the condition: For all sets A1,A2,,ArA_1, A_2, \dots, A_r with AiAj=A_i \cap A_j = \emptyset, for all iji \neq j, and k=1rAk={1,2,,m}\bigcup_{k = 1}^{r} A_k = \{ 1, 2, \dots, m \}, there exists a,bAka, b \in A_k for some kk such that 1ba1+120221 \leq \frac{b}{a} \leq 1 + \frac{1}{2022}.