That last one is going to have n minus k minus 1 possibilities. Now hopefully it will map a little bit better to the one where we had 5 flips and 3 heads. Here there was 5 possibilities for the first head, 4 possibilities for the second head. Then n is 5, 5 minus 2, you had 3 possibilities for the last head. This actually works. This is the number of spots or the number of ways that we can put 3 heads into 5 different possible buckets. Just like the last video, we don't want to over count things, because we don't care about the order.