The 40 unit squares of the 9 9-table (see below) are labeled. The horizontal or vertical row of 9 unit squares is good if it has more labeled unit squares than unlabeled ones. How many good (horizontal and vertical) rows totally could have the table?
answer is 16, (Example is very simple). assume we can do more - at least 17. Then we have at least $ (17 \cdot 5)/2=85/2=42.5$
labeled unit squares. Contradiction.
