A couple has two children. If the odds of having a boy or girl are equal, and if one of the children is a girl, what is the probability that both are girls?

GRE Quant Problem Solving
1

For this question, because we want to find the probability of getting two girls and given that one of them is already a girl, I did P(GG) = 1 * (1/2) = (1/2) which makes sense to me because one of the girls already exists but greg got 1 by 3 because there were three possible cases BG, GB, GG and only the last one satisfied the question but I don’t understand why I’m wrong.

2

You don’t know that the first child is a girl.

3

You do though right?
They said if the first child is a girl

4

They only say “one of the children” is a girl.