EX 2.2 squence of outputs

1. If we examine three welds in sequence and note the result of each examination, then an outcome for the entire experiment is any sequence of $N$ ‘s and $D$ ‘s of length 3, so $$\begin{array}{rl}\mathcal{S}=\{& NNN,NND,NDN,NDD,\\ & DNN,DND,DDN,DDD\}\end{array}$$
2. If we had tossed a thumbtack three times, the sample space would be obtained by replacing $N$ by $U$ in $\mathcal{S}$ above, with a similar notational change yielding the sample space for the experiment in which the genders of three newborn children are observed.