Question

The Smith family has 4 children that are all girls. What is the probability that the next one will be a girl?

You plan on having four children and you want all boys. If you have children, what is the probability you will get four boys?

Answer 1

The prob. that the Smith family's next child will be girl is simply 1/2

In all families with four children the prob that the four children will be all boys is (1/2)^4 = 1/16

Answer 2

Here is a principle involved.

http://www.members.cox.net/dagershaw/lol/Odds.html

I hope this helps a little more. Thanks for asking.