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list of ten numbers game

Source: VIII May Olympiad (Olimpiada de Mayo) 2002 L2 P2

September 19, 2022
combinatorics

Problem Statement

Let kk be a fixed positive integer, k10k \le 10. Given a list of ten numbers, the allowed operation is: choose kk numbers from the list, and add 11 to each of them. Thus, a new list of ten numbers is obtained. If you initially have the list 1,2,3,4,5,6,7,8,9,101,2,3,4,5,6,7,8,9,10, determine the values of kk for which it is possible, through a sequence of allowed operations, to obtain a list that has the ten equal numbers. In each case indicate the sequence.