Place eight 'X's on a 4x4 grid so that each 'X' is orthogonally bordered by an even number of 'X's and each empty square is orthogonally bordered by an odd number of 'X's.

Can 18 'X's be placed in a 6x6 grid in this manner?

Note: 'orthogonally' means horizontally or vertically

One way of doing this problem is

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Posted by ram on 2007-11-01 04:08:25