China Girls MO 2016/6
Posted: Tue Apr 18, 2017 7:06 pm
Find the greatest positive integer $m$, such that one of the $4$ letters $\text{C, G, M, O}$ can be placed in each cell of a table with $m$ rows and $8$ columns, and has the following property: For any two distinct rows in the table, there exists at most one column, such that the entries of these two rows in such a column are the same letter.