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?


closed as off-topic by Rory Daulton, Adrian Keister, Jens, Holo, user91500 Jan 15 at 6:40

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    $\begingroup$ Welcome to MathSE! You are more likely to get a good answer to your question if you follow a few guidelines. In particular, what have you tried so far, and just where are you stuck? This is not a homework-answering site: many of us want to see that you have put significant work into the problem. $\endgroup$ – Rory Daulton Jan 15 at 1:50
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    $\begingroup$ Yes, even if that is just providing further details as to precisely what part of the textbook explanation you don't follow. I would assume Olympiad problems are not your homework, but a task you are working on for enrichment. $\endgroup$ – bounceback Jan 15 at 5:06