Another Math Problem

Here is another math (probability) problem that I have discovered, that I enjoyed solving - and challenged Carlos to solve.

I'll leave the answer up to you.

Part I: Mr. Jones has two children. The older child is a girl. What is the probability that both children are girls?

Part II: Mr. Smith has two children. At least one of them is a boy. What is the probability that both children are boys?

If you want the answer, post a comment. I'll reply. Or go here.

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For the previous math problem I posted, go here.