A fair coin is flipped 3 times. What is the probability of getting at least one head?

Use the complement: the only way to get no heads is three tails, which has probability $\left(\frac{1}{2}\right)^3=\frac{1}{8}$. So $P(\text{at least one head})=1-\frac{1}{8}=\frac{7}{8}$, choice H. Listing the $8$ equally likely outcomes shows that only TTT has no heads, so $7$ of $8$ outcomes qualify. Choice F ($\frac{1}{8}$) is the probability of no heads. Choice G ($\frac{3}{8}$) is the probability of exactly one head. Choice J ($\frac{1}{2}$) is the probability of a head on a single flip.