MathDB
white, black and gray color in 7x7x7 cube

Source: 2022 South Russian Girls MO - Assara Seniors p7

March 1, 2024
Coloringcombinatoricsgeometry3D geometry

Problem Statement

In a 7×7×77\times 7\times 7 cube, the unit cubes are colored white, black and gray colors so that for any two colors the number of cubes of these two colors are different. In this case, NN parallel rows of 77 cubes were found, each of which there are more white cubes than gray and than black. Likewise, there were NN parallel rows of 77 cubes, each of which contained gray there are more cubes than white and than black, and there are also N parallel rows of 77 cubes, each of which contains more black cubes than white ones and than gray ones. What is the largest NN for which this is possible?