married couples  geometric distributionby irony of truth Tags: couples, distribution, geometric, married 

#1
Oct204, 10:22 AM

P: 93

A couple plans to continue having children until they have their first girl. Suppose the probability that a child is a girl is 0.5, the outcome of each birth is an independent event, and the birth at which the first girl appears has a geometric distribution. What is the couple's expected family size? Is the geometric pdf a reasonable model?
The expected value of a geometric dist. is 1/p = 1/0.5 = 2. My problem is the 2nd question: from my point of view.. my answer is yes. Bec. the even only concerns w/ successgirl and failureboy. Is my reason enough to say that gd. is the reasonable model? =) 



#2
Oct204, 05:43 PM

Sci Advisor
P: 5,939

The probability that they will have n children (n >=1) is .5^{n}. I presume that is a case of geometric distribution.



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