You are correct that there are 8 possibilities:
BBB
BBG
BGB
BGG
GBB
GBG
GGB
GGG
We'll assume boy or girl is equally likely. (in fact it's not quite 50:50 but pretty close).
Each possibility has a probability of 1/8
Three of those listed have exactly two girls so P(two girls) = 1/8 + 1/8 + 1/8 = 3/8
There a formula for this:
p is the probability of an event; q = (1-p) is the probability of the event not happening; n is the total number of events; r is the number that we want.
You can find more on this here:
http://www.mathsisfun.com/data/binomial … ution.html
Bob
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