The probability of getting at least one head in three flips is the same thing as the probability of not getting all tails in three flips. Let me write in three flips. So what's the probability of not getting all tails? Well, that's going to be 1 minus the probability of getting all tails. And since it's three flips, it's the probability of tails, tails, and tails. Because any of the other situations are going to have at least one head in them. And that's all of the other possibilities.