MathDB
Colors and *sigh* 207 boxes

Source: Turkey JBMO TST 2024 P8

May 13, 2024
combinatoricsgame strategy

Problem Statement

There is 207207 boxes on the table which numbered 1,2,,2071,2, \dots , 207 respectively. Firstly Aslı puts a red ball in each of the 100100 boxes that she chooses and puts a white ball in each of the remaining ones. After that Zehra, writes a pair (i,j)(i,j) on the blackboard such that 1ij2071\leq i \leq j \leq 207. Finally, Aslı tells Zehra that for every pair; whether the color of the balls which is inside the box which numbered by these numbers are the same or not. Find the least possible value of NN such that Zehra can guarantee finding all colors that has been painted to balls in each of the boxes with writing NN pairs on the blackboard.