Here is a square sequence of numbers.

392?
6  3
7  4
?817

What are the two question marks?

Let x = the top right ?
Let y = the bottom left ?

The sum of the top row is 3+9+2+x = 14+x
The sum of the right side is 3+4+7+x = 14+x
The sum of the bottom row is 8+1+7+y = 16+y
The sum of the left row is 3+6+7+y = 16+y

So if x=y+2 then all the rows have the same sum.

The middle two rows contain four numbers: 6,3,7,4. Of these numbers two of them appear as corner values (3&7). The other two (6&4) have a difference of 2, so if x=6 and y=4 then all the rows have the same values and the corner values are the same as those that appear in the middle two rows.

This makes the finished square...

3926
6__3
7__4
4817

Posted by fwaff on 2003-09-09 10:54:40