Pluses and minuses in a 30 x 30 table
Source: Baltic Way 2006
December 4, 2010
combinatorics proposedcombinatorics
Problem Statement
pluses and minuses are placed in a table in such a way that each row and each column contains at most signs. (No cell contains more than one sign.) For every plus we count the number of minuses in its row and for every minus we count the number of pluses in its column. Find the maximum of the sum of these numbers.