In the Real World
Let's say you're working at A & F in the mall. You're in charge of shirts, because your manager thinks you have real promise. Don't let her down!
First, you're doing an inventory of red polo shirts. There are two kinds, with a logo and without a logo, and you have some of each kind in each of three sizes: small, medium, and large. You count them up as follows:
With logo: 3 small, 5 medium, 4 large
Without logo: 2 small, 4 medium, 6 large
You can enter your data into a matrix to keep track of those pesky shirts, where "with logo" is row one, "without logo" is row two, small is column one, medium is column two, and large is column three:
Since you're so amazing at inventory, you go ahead and count the blue polo shirts too:
With logo: 0 small, 7 medium, 1 large
Without logo: 3 small, 3 medium, 0 large
And the blue shirt matrix looks like this:
Naturally, your manager wonders how many shirts with logos there are in either color for each size. No problem! You've got it all laid out, matrix-style.