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LostInParadise's avatar

Can you find the winning strategy for this simple game?

Asked by LostInParadise (31907points) June 28th, 2011

There are two players, A and B. A has a 6 by 6 grid on a piece of paper and B has a row of 6 boxes.
A goes first and fills in the boxes in the first row with X or O.
Then B fills in the first box of the row with either X or O.
A continues to fill in a row at a time with X and O and B responds by filling the next box in the row with X or O.

B’s objective is to duplicate one of the A’s rows and A objective is to prevent this.

1. What is a winning strategy for B?
2. If B makes the wrong first move, how can A assure a win?

I lifted this problem from the book Heart of Mathematics. The first part of the problem is a good introduction to working with infinity, which is one of the areas covered in the book. I found out about the book from a liberal arts math course I heard about. From the Amazon reviews, it appears that there are a number of such courses that use the book. I got a copy of it from the library, because I have an interest in math education and because I thought I might fill in a few gaps in my own math education. So far I have mixed opinions on the book.

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7 Answers

LostInParadise's avatar

Correction: A’s objective is to have one of the rows in the grid duplicate B’s row and B’s objective is to prevent this.

6rant6's avatar

Are you sure your rules are correct?

LostInParadise's avatar

With the correction. What difficulty are you having?

6rant6's avatar

Where are these marks: “A goes first and fills in the boxes in the first row with X or O.Then B fills in the first box of the row with either X or O.”
A fills in the row? Then B fills in a box? This is the same row? Next row? When does the game end?

flutherother's avatar

B can’t fail to win if he writes the opposite symbol to A. If A starts his first row with an X, B should write O, if A starts his second row XO B should write XX. That way B is always one step ahead of A and will win the game.

If B were to make an error and write the same symbol he is doomed. For example if A writes X and B also writes X A is then one step ahead. If A had written XO in row one he should now write XX in row two and B has no choice but to copy one or the other and so on to the end of the game.

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