posted by Chuck .
we are working on a puzzle similar to a magic square. 9 boxes are arranged in an X with the center box being shared by both diagonals. the goal is to use each integer 1-9 one time so that each diagonal sums to 26 and the 4 corners sum to 26.
1 - 3 - 7 - 6 - 9
2 - 4 - 7 - 8 - 5
7 is at the intersection and gets used twice.
Since the sum of all digits is 45, and you want more than half of that for the total on both rows, the shared digit in the middle had to be slightly above the mean (5).
I tried 6 and then 7. The rest was easy.