MathDB
Tiling game

Source: Iran MO 2023 3rd round , Combinatorics exam P3

August 19, 2023
combinatoricsceiling function

Problem Statement

There's infinity of the following blocks on the table:11,12,13,..,1n1*1 , 1*2 , 1*3 ,.., 1*n. We have a nnn*n table and Ali chooses some of these blocks so that the sum of their area is at least n2n^2. Then , Amir tries to cover the nnn*n table so that none of blocks go out of the table and they don't overlap and he wanna maximize the covered area in the nnn*n table with those blocks chosen by Ali. Let kk be the maximum coverable area independent of Ali's choice. Prove that: n2n24kn2n28n^2 - \lceil \frac{n^2}{4} \rceil \leq k \leq n^2 - \lfloor \frac{n^2}{8} \rfloor
*Note : the blocks can be placed only vertically or horizontally.