Three unbiased coins are tossed. What is the probability of getting at least 2 tails?

Answer: Option B

S = {HHH, HHT, HTH, HTT, THH, THT, TTH, TTT}
E = {HTT, THT, TTH, TTT}
$$\begin{array}{rl}& \text{n(S) = 8}\\ & \text{n(E) = 4}\\ & \text{P(E) = }\frac{\text{n(E)}}{\text{n(S)}}\\ & =\frac{\text{4}}{8}\\ & =\text{0}\text{.5}\end{array}$$