16 checkers are placed on an 8 by 8 checkerboard, no two checkers on the same square. Show that some four of the 16 checkers are on the vertices of a parallelogram with positive area.

...on how to make proofs for problems such as this. I certain that I know the answer, but I lack the skills to prove why.

Posted by Charley on 2005-06-12 18:05:57