I am picking 4, exactly 4, of the 6 heads. Sorry, I'm picking 4 of exactly 6 of the flips to end up heads. I'm choosing which of the flips get selected, so to speak. So it's essentially, there are going to be, out of 6 flips, I'm choosing, as the god of probability, 4 to be heads. So that's the number of combinations, the number of unique combinations, where you have 4 out of 6 heads, times the probability of each of the combinations, which is 1 half to the 6th power. Well, let's 6 choose 4. That's 6 factorial over 4 factorial times 6 minus 4 factorial, so that's 2 factorial.