Solution
= Solution
The successful ordered outcomes are $TTH$, $THT$ and $HTT$. Each has <probability> $1/8$ by <independence>, and these <events> are <mutually exclusive events>[mutually exclusive]. Adding their <probabilities> gives
$$
\boxed{\mathbb P(\text{exactly two tails})=\frac38}.
$$
Equivalently, the <binomial distribution> gives $\binom32(1/2)^2(1/2)=3/8$.