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A family has two children. If [tex]$B$[/tex] represents a boy and [tex]$G$[/tex] represents a girl, the set of outcomes for the possible genders of the children is [tex]$S = \{BB, BG, GB, GG\}$[/tex], with the oldest child listed first in each pair. Let [tex]$X$[/tex] represent the number of times [tex]$G$[/tex] occurs.

Which of the following is the probability distribution [tex]$P_X(x)$[/tex]?

\begin{tabular}{|c|c|}
\hline [tex]$x$[/tex] & [tex]$P_X(x)$[/tex] \\
\hline 0 & 0.25 \\
\hline 1 & 0.5 \\
\hline 2 & 0.25 \\
\hline
\end{tabular}

\begin{tabular}{|c|c|}
\hline [tex]$X$[/tex] & [tex]$P_X(x)$[/tex] \\
\hline 0 & 0.33 \\
\hline 1 & 0.33 \\
\hline 2 & 0.33 \\
\hline
\end{tabular}

\begin{tabular}{|c|c|}
\hline [tex]$X$[/tex] & [tex]$P_X(x)$[/tex] \\
\hline 0 & 0.25 \\
\hline 1 & 0.75 \\
\hline 2 & 0 \\
\hline
\end{tabular}

\begin{tabular}{|c|c|}
\hline [tex]$x$[/tex] & [tex]$\operatorname{Pr}(x)$[/tex] \\
\hline 0 & 0 \\
\hline
\end{tabular}


Sagot :

To determine the probability distribution [tex]\(P_X(x)\)[/tex] for the number of times a girl (G) occurs in the family of two children, we start by enumerating all possible gender outcomes for the two children:

1. [tex]\(BB\)[/tex] (no girls)
2. [tex]\(BG\)[/tex] (one girl)
3. [tex]\(GB\)[/tex] (one girl)
4. [tex]\(GG\)[/tex] (two girls)

Given this set [tex]\(S = \{BB, BG, GB, GG\}\)[/tex], we calculate the probability for each value of [tex]\(x\)[/tex], where [tex]\(x\)[/tex] is the number of girls (G):

Step-by-Step Solution:

1. Count the occurrences for each value of girls [tex]\(x\)[/tex]:

- 0 girls (x = 0): There is only one combination where there are no girls, which is [tex]\(BB\)[/tex].
[tex]\[ P_X(0) = \frac{1}{4} \][/tex]

- 1 girl (x = 1): There are two combinations where there is exactly one girl, which are [tex]\(BG\)[/tex] and [tex]\(GB\)[/tex].
[tex]\[ P_X(1) = \frac{2}{4} \][/tex]

- 2 girls (x = 2): There is only one combination where there are two girls, which is [tex]\(GG\)[/tex].
[tex]\[ P_X(2) = \frac{1}{4} \][/tex]

2. Calculate the probabilities:

- [tex]\(P_X(0) = \frac{1}{4} = 0.25\)[/tex]
- [tex]\(P_X(1) = \frac{2}{4} = 0.5\)[/tex]
- [tex]\(P_X(2) = \frac{1}{4} = 0.25\)[/tex]

Thus, the resulting probability distribution for [tex]\(X\)[/tex] is:
[tex]\[ \begin{array}{|c|c|} \hline x & P_X(x) \\ \hline 0 & 0.25 \\ \hline 1 & 0.5 \\ \hline 2 & 0.25 \\ \hline \end{array} \][/tex]

After comparing with the given options in the question, we find that the correct probability distribution matches the first tabular option:
[tex]\[ \begin{tabular}{|c|c|} \hline x & P_X(x) \\ \hline 0 & 0.25 \\ \hline 1 & 0.5 \\ \hline 2 & 0.25 \\ \hline \end{tabular} \][/tex]