MathDB
Nasty 5x5 table

Source: 2019 CSMO Grade 11 P4

July 30, 2019
combinatoricsBashingmatrix

Problem Statement

Let XX be a 5×55\times 5 matrix with each entry be 00 or 11. Let xi,jx_{i,j} be the (i,j)(i,j)-th entry of XX (i,j=1,2,\hdots,5). Consider all the 2424 ordered sequence in the rows, columns and diagonals of XX in the following: \begin{align*} &(x_{i,1}, x_{i,2},\hdots,x_{i,5}),\ (x_{i,5},x_{i,4},\hdots,x_{i,1}),\ (i=1,2,\hdots,5) \\ &(x_{1,j}, x_{2,j},\hdots,x_{5,j}),\ (x_{5,j},x_{4,j},\hdots,x_{1,j}),\ (j=1,2,\hdots,5) \\ &(x_{1,1},x_{2,2},\hdots,x_{5,5}),\ (x_{5,5},x_{4,4},\hdots,x_{1,1}) \\ &(x_{1,5},x_{2,4},\hdots,x_{5,1}),\ (x_{5,1},x_{4,2},\hdots,x_{1,5}) \end{align*} Suppose that all of the sequences are different. Find all the possible values of the sum of all entries in XX.