All about flooble | fun stuff | Get a free chatterbox | Free JavaScript | Avatars    
perplexus dot info

Home > Games
The Central Cell (Posted on 2004-04-16) Difficulty: 2 of 5
Prove that the central cell (the number in the middle cell) of any 3x3 magic square is always one-third the magic constant (the sum of any side, either 2 major diagonals, or either center row in the magic square).
Show that in any larger square (n x n), the central cell does not need to be 1/n the magic constant.

See The Solution Submitted by Victor Zapana    
Rating: 4.5000 (4 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
Some Thoughts General counter-example | Comment 6 of 11 |

For all larger magic squares with an odd numbered side length, I can find a general counter-example using only ones and zeroes.  If every number must be different, than add the counter-example to a magic square filled with even numbers to get your new counter-example.

To get the general counter example, start with a 5 x 5 square like this:


The magic constant is 1, but the center is not 1/5.

To generate a 7 x 7 counter example, insert new rows between the 2nd and 3rd rows, and the 4th and 5th rows.  Insert two new columns in the same places.  Fill the rows with zeroes, except for the upper right and lower left intersections, which will have ones.


Noticed that the positions of the new rows and columns are:
1) between the middle row/column and the one before it
2) and between the last row/column and the one before it

Before regenerating a new square, turn this one around 180 degrees, then follow the same steps as before.  Continue to regenerate new squares this way, turning upside-down, filling the new columns and rows the same way as before.  This should give a counter-example for all odd-numbered squares above 5.

I haven't checked, so I could be wrong on this.  There may be a problem later on with having diagonals add up, and it might not work after all.

Added in:
After trying it a few times, I have become convinced that it works, which is wonderful, except I don't have prooof.

Edited on April 16, 2004, 6:01 pm
  Posted by Tristan on 2004-04-16 17:47:12

Please log in:
Remember me:
Sign up! | Forgot password

Search body:
Forums (0)
Newest Problems
Random Problem
FAQ | About This Site
Site Statistics
New Comments (1)
Unsolved Problems
Top Rated Problems
This month's top
Most Commented On

Copyright © 2002 - 2018 by Animus Pactum Consulting. All rights reserved. Privacy Information