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Math Help - Please Help No Idea!!

  1. #1
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    Please Help No Idea!!

    I HAVE NO IDEA ON THIS ONE IM SO LOST

    A geologist is using seismographs to test for oil. It is found that if oil is present, the test gives a positive result 95% of the time, and if oil is not present, the test gives a positive result 2% of the time. Oil is actually present in 1% of the cases tested. If the test shows positive, what is the probability that oil is present??????

    (solved in either a tree diagram, contingency table or proper formula and substitution)


    PLEASE HELP!!!
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  2. #2
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    Quote Originally Posted by jobear View Post
    I HAVE NO IDEA ON THIS ONE IM SO LOST

    A geologist is using seismographs to test for oil. It is found that if oil is present, the test gives a positive result 95% of the time, and if oil is not present, the test gives a positive result 2% of the time. Oil is actually present in 1% of the cases tested. If the test shows positive, what is the probability that oil is present??????

    (solved in either a tree diagram, contingency table or proper formula and substitution)


    PLEASE HELP!!!
    You need to get Pr(oil|+ve).

    A tree diagram is the easiest approach to take.

    Start with the oil:

    /oil (0.01)
    \no oil (0.99)

    and then add the +ve test and -ve test branches for each.

    You should get as the answer:

     \frac{(0.01)(0.95)}{(0.01)(0.95) + (0.99)(0.02)} = .......

    Alternatively, you can chew on what the good Captain has said at your double post.
    Last edited by mr fantastic; March 8th 2008 at 02:30 AM. Reason: Noted the double posting
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