Just like the last video, we don't want to over count things, because we don't care about the order. We don't want to differentiate one ordering of heads. I'm just going to use these letters to differentiate the different heads. We don't want to differentiate this from this. Heads A, heads B, or any of the other orderings of this. What we need to do is divide this number so that we don't count all of those different orderings. We need to divide this by the different ways that you can order k things.