# Variation of Boy/Girl Birth Problem [closed]

Parents keep having children until they have one girl, at which point they stop; and babies are girls with probability 0.49.

If we select a child uniformly at random (from the entire population of children), what's the probability he or she has exactly one sibling?

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I thought this would just be probability of BG 51/100*49/100 but it isn't.

P = P(G)P(BG| Choose G) + P(B)P(BG|choose B)

• This isn't a puzzle, agreed, but I don't think this is a math textbook problem either. This is a population simulation problem, and it looks to be of the particular type which tends to go haywire in wildly interesting ways depending on the exact initial parameters and included features of the simulation. Feigenbaum constants may also play a role here. Or then again, maybe not, I'm not really an expert on this. :-) – Bass Jun 11 '18 at 14:47