This is a question from the 1998 math olympiad I found 2 solutions in the following places: book1 pg.32 book2 pg.163 however, I was having trouble understanding them. Any help would be appreciated
There is a 98 × 98 chessboard, colored in the usual way. One can select any rectangle with sides on the lines of the chessboard and as a result, the colors in the selected rectangle switch (black becomes white and white becomes black). What is the minimum number of changes needed to make the chessboard all one color?