mathematics, posts by tag: combinatorics - LiveJournal

a 5 x 4 binary matrix must

a) have two ones in each column
b) have at least one one in each row

How many such matrices are there?
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UPDATE: shoot. cheeser1 solved it. Nice work!!!!

We're covering this in my combinatorics class and I am just wondering what some of the applications will be and how this relates to combinatorics.