Probability

I'm trying to teach myself probability, but it's really difficult for me to understand.

I'm trying this question from a textbook I've downloaded online, and I just can't seem to wrap my head around it.

Question 1. a) There is a family of 3 children. You saw one of the children, and it's a girl. What's the probability that all of them are girls?

1. b) You saw another child. You're not sure if it's the same girl you saw. What's the probability that all of the children are girls? Is it the same as question 1. a)?

This all depends on how insane you want to get on accuracy.  There's a slight difference in male:female ratio, (although it's not clear on if that's by virtue of other factors, or differing birth rate.  Someone might know, I don't.). For the scope of the question, I'll assume it's 50:50.

As for b., well, yes it's the same question, unless you want to take the one female child into account based on how many female children there are in the world and alter the probability of the other 2 being female by an infinitesimally small amount.

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