A couple has two children, one of whom is a girl. If the probability of having a girl or a boy is 50%, what is the probability that the couple has two daughters?
Choose the most appropriate option
A) 1/8
B) 1/4
C) 1/3
D) 1/2
E) 2/3
First child ---- Second child:   B ---------------------------- B;   B ---------------------------- G;   G ---------------------------- B;   G ---------------------------- G.   We know that one if the kids is a girl. So, we have one of the three cases in red. Each case there is equally likely (each has the probability of 1/2*1/2=1/4). So, the probability of GG is 1/3.   Answer: 1/3.
<result>C</result>
A couple has two children, one of whom is a girl. If the probability of having a girl or a boy is 50%, what is the probability that the couple has two daughters?