I'm taking a crack at learning probability and statistics starting from the basics. Anyways here is the question. --- A fair coin is tossed 10 times and the sequence of scores recorded. How many sequences are there? How many sequences are there that contain exactly 3 heads? --- The first one is no problem. I understand it. It simply is 2^10 = 1024 possible sequences. The second one is the one i have trouble dealing with. How do you compute it with that special case added in? The answer given is 120.