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Math Help - another probability question, i am doing it wrong as i get 1.5

  1. #1
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    another probability question, i am doing it wrong as i get 1.5

    suppose for simplicity that the number of children in a family is 1, 2, or 3 with probability 1/3 for each. Little Bobby has no sisters. What is the probability that he is an only child.

    I got 1.5 which is CLEARLY wrong.

    let E= there are no sisters
    F = being an only child

    Probably of there being no sisters is 3/14 and being only child is 2/14

    P(e/f) = (3/14)/(2/14) = 1.5 which is wrong.
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  2. #2
    kin
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    Quote Originally Posted by SydneyBristow View Post
    suppose for simplicity that the number of children in a family is 1, 2, or 3 with probability 1/3 for each. Little Bobby has no sisters. What is the probability that he is an only child.

    I got 1.5 which is CLEARLY wrong.

    let E= there are no sisters
    F = being an only child

    Probably of there being no sisters is 3/14 and being only child is 2/14

    P(e/f) = (3/14)/(2/14) = 1.5 which is wrong.
    the required probability =P(f | e)= P( f and e) / P(e)
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  3. #3
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    how did you derive that the probability of there being no sisters is 3/14 and being only child is 2/14?
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