Jane 的孩子

在“至少一个是女儿”的条件下，两孩样本空间为

$$\{(b,g),(g,b),(g,g)\},$$

三种等可能，其中只有 $(g,g)$ 满足两个女儿。

因此概率为 $1/3$。

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Original Explanation

The sample space of two children given at least one child is a daughter is $\Omega = \{ (b,g), (g,b), (g,g)\}$, where $(b,g)$ means that the older child is a boy and the younger child is a girl. Thus, the probability that Jane has two daughters is $\frac{1}{3}$.