If you're trying to figure out the number of permutations where you could put n people in r seats, or the number of permutations, you could put n people in r seats, and there's other notations as well. Well this is just going to be n factorial over n minus r factorial. Here n was five, r was three, and five minus three is two. Now, you'll see this in a probability or statistics class, and people might memorize this thing, it seems like this kind of daunting thing. I'll just tell you right now, the whole reason why I just showed this to you is so that you could connect it with what you might see in your textbook, or what you might see in a class, or when you see this type of formula, you see that it's not coming out of, it's not some type of voodoo magic, but I will tell you that for me, personally, I never use this formula. I always reason it through, because if you just memorize the formula, you're always going to wait, does this formula apply there? What's n, what's r?