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Operation on a 3*3 table

Source: North Korea Team Selection Test 2013 #4

May 17, 2014
combinatorics proposedcombinatorics

Problem Statement

Positive integers 1 to 9 are written in each square of a 3×3 3 \times 3 table. Let us define an operation as follows: Take an arbitrary row or column and replace these numbers a,b,c a, b, c with either non-negative numbers ax,bx,c+x a-x, b-x, c+x or a+x,bx,cx a+x, b-x, c-x, where x x is a positive number and can vary in each operation. (1) Does there exist a series of operations such that all 9 numbers turn out to be equal from the following initial arrangement a)? b)? a)123456789) a) \begin{array}{ccc} 1 & 2 & 3 \\ 4 & 5 & 6 \\ 7 & 8 & 9 \end{array} ) b)285934671) b) \begin{array}{ccc} 2 & 8 & 5 \\ 9 & 3 & 4 \\ 6 & 7 & 1 \end{array} ) (2) Determine the maximum value which all 9 numbers turn out to be equal to after some steps.