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Math Help - Probabilty question

  1. #1
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    Probability question

    hey,

    i have a probabilty question to solve but i am not sure if i have interpreted the text in the correct way.


    1. the prob. of a mother murdering her own infant is 1/100.000 pa.
    2. the prob. of an infant dieing of sids is 1/8500 pa.
    3. in such situations, 1 in 20 cases of bruising are by attempted or actual murder. 1 in 100 caes of bruising are due to efforts of resusicatete.
    4. the prob. of finding signs of fatal disease give sids is 1 in 20. otherwise the prob. of finding signs of fatal disease give murder is 1 in 1000.

    I have the following:
    P(murder) = 1/100000
    P(dieing of sids) = 1/8500
    P(bruising|murder) = 1/20
    P(bruising|deceased) = 1/100
    P(disease|sids) = 1/20
    P(disease|murder) = 1/1000

    Have I interpreted this in a right way?

    In order to solve (murder and sids are independent events):

    whats the prob. of:

    a: child 1 was murdered? (Answer: 1/100000?)
    b: child 2's death was due to sids? (Answer: 1/8500?)
    c: both child 1 and child 2 where murdered? (Answer: 1/100000 * 1/100000?)
    d: one child was murdered and the other died due to sids? (Answer: 1/100000 + 1/8500 - (1/100000 * 1/100000))?

    Is that correct?

    thanks in advance
    Last edited by sanv; February 2nd 2009 at 02:41 AM.
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  2. #2
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    Quote Originally Posted by sanv View Post
    hey,

    i have a probabilty question to solve but i am not sure if i have interpreted the text in the correct way.


    1. the prob. of a mother murdering her own infant is 1/100.000 pa.
    2. the prob. of an infant dieing of sids is 1/8500 pa.
    3. in such situations, 1 in 20 cases of bruising are by attempted or actual murder. 1 in 100 caes of bruising are due to efforts of resusicatete.
    4. the prob. of finding signs of fatal disease give sids is 1 in 20. otherwise the prob. of finding signs of fatal disease give murder is 1 in 1000.

    I have the following:
    P(murder) = 1/100000
    P(dieing of sids) = 1/8500
    P(bruising|murder) = 1/20
    P(bruising|deceased) = 1/100
    P(disease|sids) = 1/20
    P(disease|murder) = 1/1000

    Have I interpreted this in a right way?

    In order to solve (murder and sids are independent events):

    whats the prob. of:

    a: child 1 was murdered? (Answer: 1/100000?)
    b: child 2's death was due to sids? (Answer: 1/8500?)
    c: both child 1 and child 2 where murdered? (Answer: 1/100000 * 1/100000?)
    d: one child was murdered and the other died due to sids? (Answer: 1/100000 + 1/8500 - (1/100000 * 1/100000))?

    Is that correct?

    thanks in advance
    a, b, c: correct.

    For d,

    Pr(one murdered and one died of sids) =
    Pr(child1 murdered and child2 died of sids) + Pr(child1 died of sids and child2 murdered).
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  3. #3
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    I am stuck on calculating the following probabilities:

    P(bruising|murder AND sids)
    P(bruising|~(murder AND sids))

    Is there a way to calculate those probabilities?

    thanks in advance.
    Last edited by sanv; February 16th 2009 at 01:30 AM.
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  4. #4
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    They could be solved by Bayes theorem but I don't seem to have all the info?
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