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

When a fair coin is tossed two times, the sample space $S$ representing all possible outcomes is:
$$S=\{HH,HT,TH,TT\}$$

The total number of possible outcomes is $n(S)=4$.

Let $E$ be the event of getting at least one head. This includes outcomes with exactly one head or two heads:

$$E=\{HH,HT,TH\}$$

The number of favorable outcomes is $n(E)=3$.

The probability $P(E)$ of the event is given by the formula:

$$P(E)=\frac{n(E)}{n(S)}=\frac{3}{4}$$

Thus, the probability of getting at least one head is $\frac{3}{4}$.