What is the least number of unit squares that you need to remove from this 5 by 3 checker board in order to make it impossible for anyone to put an "X" in 3 remaining squares to make a connected vertical, horizontal, or diagonal set of 3 (a set that looks like a "win" in a standard Tic Tac Toe game)?
Hint: Try the problem on a smaller board first.
by Brilliant Staff
