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ggrree

  • 3 years ago

this should be an easy problem, but I can't work out the right answer for the life of me: A couple decides to have children until they get a girl, but agree that they will not have more than 3 children, even if they are all boys. (assume boys and girls are equally likely) What is a the probability of each outcome? What is the expected number of children? What is the expected number of boys? What is the standard deviation of the number of kids?

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  1. ggrree
    • 3 years ago
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    from what I understand, the possible outcomes are: 1 girl: (1/2) , 1 boy and then 1 girl (1/2 * 1/2), 2 boys and 1 girl (1/6) or 3 boys (1/6). Clearly something is wrong here because those probabilities do not add up to 1, what am I missing?

  2. anonymous
    • 3 years ago
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    what are the possible outcomes?

  3. anonymous
    • 3 years ago
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    oh i see your mistake \[\frac{1}{2}\times \frac{1}{2}\times \frac{1}{2}=\frac{1}{8}\]

  4. ggrree
    • 3 years ago
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    LOL

  5. ggrree
    • 3 years ago
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    THANKS! I thought 1/2 * 1/2 * 1/2 was 1/6... wow.

  6. anonymous
    • 3 years ago
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    damned arithmetic

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