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Putnam 2024 A3

  • Session A

Let SS be the set of bijections T ⁣:{1,2,3}×{1,2,…,2024}→{1,2,…,6072}T \colon \{1,2,3\} \times \{1,2,\dots,2024\} \to \{1,2,\dots,6072\} such that T(1,j)<T(2,j)<T(3,j)T(1,j) < T(2,j) < T(3,j) for all j∈{1,2,…,2024}j \in \{1,2,\dots,2024\} and T(i,j)<T(i,j+1)T(i,j) < T(i,j+1) for all i∈{1,2,3}i \in \{1,2,3\} and j∈{1,2,…,2023}j \in \{1,2,\dots,2023\}. Do there exist aa and cc in {1,2,3}\{1,2,3\} and bb and dd in {1,2,…,2024}\{1,2,\dots,2024\} such that the fraction of elements TT in SS for which T(a,b)<T(c,d)T(a,b) < T(c,d) is at least 1/31/3 and at most 2/32/3?

Curated text Kedlaya Putnam archive. Quoted with source.

Solutions

Human solution Solution 1 by Manjul Bhargava, Kiran Kedlaya and Lenny Ng

The terms of the source let olymmath link to this solution but not copy it. Read the solution (Kedlaya Putnam archive).

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