In the diagram formed of twenty O’s below, in how many ways may four be selected such that they form a square?
What is the least number of O’s that may be removed such that none of these squares remains intact?
O O
O O
O O O O O O
O O O O O O
O O
O O
Note: the horizontal and vertical spacing should be equal.
(In reply to
re: Solution by Federico Kereki)
Actually, I think I made another mistake also, I think we would have to get rid of 7 o's to eliminate the possibilty of making any squares, including the 2 extra you found.

Posted by tomarken
on 20060510 09:57:58 