Just not to confuse you, let me write it like this. You'll have n spots for that first head, n minus 1 spots for that second head. Then you keep going and you're going to have a total of these k things you're multiplying. 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.