Question 4613
The logic here is almost what you wrote, but then you make up some "Maggie logic" :-).

Consider all the possibilities for the 3 kids, with the eldest written first, then the second oldest then the youngest:


BBB
BBG
BGB
BGG
GBB
GBG
GGB
GGG


These are all the possible variations for the 3 children. How many of these outcomes are 3 girls? just 1. Out of how many possible outcomes? 8...answer is therefore 1/8!


Mathematically, we can say:


P(3 girls) = P(first is girl) and P(second is girl) and P(third is girl)
P(3 girls) = 1/2 and 1/2 and 1/2 since for each child the probability of a girl is, yes, 1 out of 2.


But what about the "and". Well, in probability and means multiply, so we get P(3 girls) = 1/2 * 1/2 * 1/2, which again is 1/8.


Hope this helps


jon