Question

In tossing a fair coin twice, find the probability of getting exactly one tail

Answer 1

When a fair coin is tossed twice, $S=\{HH,TT,HT,TH\}\therefore n\left(S\right)=4$
Let $D$ be the event of getting exactly one tail
$D=\{HT,TH\}\therefore n\left(D\right)=2$
$\therefore P\left(D\right)=\frac{n\left(D\right)}{n\left(S\right)}=\frac{2}{4}$