1993 IMO Problems/Problem 3

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Problem

On an infinite chessboard, a game is played as follows. At the start, $n^2$ pieces are arranged on the chessboard in an $n$ by $n$ block of adjoining squares, one piece in each square. A move in the game is a jump in a horizontal or vertical direction over an adjacent occupied square to an unoccupied square immediately beyond. The piece which has been jumped over is removed. Find those values of $n$ for which the game can end with only one piece remaining on the board.

Video Solution

This is a very beautifully done video solution: https://www.youtube.com/watch?v=eAROaUpkgRo Even though he made a mistake when reducing the 5x5 to a 2x2 as someone pointed out in the comments.

Solution

File:IMO1993 Label n1r.gif File:IMO1993 Label n2r.gif File:IMO1993 Label n3r.gif File:IMO1993 Label n4r.gif File:IMO1993 Label n5r.gif

IMO1993 P3 n1r.gif IMO1993 P3 n2r.gif IMO1993 P3 n3r.gif IMO1993 P3 n4r.gif IMO1993 P3 n5r.gif


File:IMO1993 Label n6r.gif File:IMO1993 Label n7r.gif File:IMO1993 Label n8r.gif File:IMO1993 Label n9r.gif File:IMO1993 Label n10r.gif

IMO1993 P3 n6r.gif IMO1993 P3 n7r.gif IMO1993 P3 n8r.gif IMO1993 P3 n9r.gif IMO1993 P3 n10r.gif


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See Also

1993 IMO (Problems) • Resources
Preceded by
Problem 2
1 2 3 4 5 6 Followed by
Problem 4
All IMO Problems and Solutions