+ Reply to Thread
Results 1 to 10 of 10

Thread: Help!! Probability ?????????????

  1. #1
    Points: 5,009, Level: 45
    Level completed: 30%, Points required for next Level: 141

    Posts
    5
    Thanks
    0
    Thanked 0 Times in 0 Posts

    Help!! Probability ?????????????




    I have a problem and need some step to step computation and a bit of explanantion. Have deadine of tomorrow

    Here's the problem:
    Oil company purchase land in Alaska..Preliminary geograhic studies assigned the following:

    P(high-quality oil) = .50
    P(medium -quality oil) .20
    P(no oil) = .30

    (a) What is the probaility of finding oil ?
    (b) After 200 feet of drilling on the first well, a soil test is taken. The probabilities of finding the particular type of soil identified by the test follow.

    p(soil /high quality oil) = .20
    p(soil/medium-quality oil) = .80
    P(soil/no oil) = .20

    How should the firm interpret the soil test? What are the revised probabilities, and what is the new probability of finding the oil?

    HELP PLEASE !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

    Thanks
    E

  2. #2
    TS Contributor
    Points: 17,636, Level: 84
    Level completed: 58%, Points required for next Level: 214
    JohnM's Avatar
    Posts
    1,948
    Thanks
    0
    Thanked 6 Times in 5 Posts
    Elizer,

    What have you attempted so far?

    For part (a), it is simply = 1 - P(no oil).

    For part (b), this looks like a situation for Bayes formula, i.e.,

    the revised probabilities would be:

    P(high-quality oil | soil)
    P(medium-quality oil | soil)
    P(no oil | soil)

  3. #3
    Points: 5,009, Level: 45
    Level completed: 30%, Points required for next Level: 141

    Posts
    5
    Thanks
    0
    Thanked 0 Times in 0 Posts

    Response

    John:

    Thank you for responding!

    I haven't attempt the problem. I was out sick for this day of class and my tutoring session is not schedule until next week, but I need to understand and do this problem in order to move ahead to the next problems. I read the problem and thought that, they did not give me enough information to complete it.

    Yes, part (b) we are suppose to use Bayes theorem!

    For clarification:

    For Part A, How would I show I show it as a fraction!
    Would it be 1-.30 = .7[/B]

    For Part B, How would I apply Bayes theorem!

    Thanks
    E

  4. #4
    TS Contributor
    Points: 17,636, Level: 84
    Level completed: 58%, Points required for next Level: 214
    JohnM's Avatar
    Posts
    1,948
    Thanks
    0
    Thanked 6 Times in 5 Posts
    for part (a), you could just report it as 0.7 or 7/10

    for part (b), Bayes formula is:

    event A = particular type of soil
    event B = particular type of oil

    P(B|A) = P(A|B)*P(B) / [ P(A|B)*P(B) + P(A|B')*P(B') ]

    What Bayes' formula does is it modifies or revises the probability of the occurrence of an event, based on "additional" information. Originally, the probability of high-quality oil was tought to be 0.5. Then they took a soil sample 200 feet down, and this is the "additional" information. You are asked to determine how this additional information revises the probability of an event.

  5. #5
    Points: 5,009, Level: 45
    Level completed: 30%, Points required for next Level: 141

    Posts
    5
    Thanks
    0
    Thanked 0 Times in 0 Posts
    Good Morning:

    John I attempt to use Bayes theorem last night in finding the new probability of oil. Can you verify if I calculated this correctly?

    I use .20 for (A) and .80 for B

    Using Bayes formula I calculate it as 1.0 x .80 / 1.0 x .80 + 1.0 x .80 = 1.44

    No sure if this is done right!

    Thanks
    E

  6. #6
    Admin
    Points: 20,637, Level: 90
    Level completed: 58%, Points required for next Level: 213
    quark's Avatar
    Location
    Canada
    Posts
    479
    Thanks
    25
    Thanked 196 Times in 73 Posts
    Good morning Elizer,

    In the denominator of the Bayes formula, you have P(A|B)*P(B) + P(A|B')*P(B'), the second part is different from the first part. B' is the complement of B, P(B')=1-P(B).

  7. #7
    Points: 5,009, Level: 45
    Level completed: 30%, Points required for next Level: 141

    Posts
    5
    Thanks
    0
    Thanked 0 Times in 0 Posts
    Thank you for the explanantion: So can you tell me if I calulate it correctly!

    For P(A/B') would be 1-.80(A) = .20(B). so then I inputted the information into the formula as:

    1.0 x .80 / 1.0 x .80 + .40 x .20 = .72

    I am due to attend class in the next 15 minutes

  8. #8
    Admin
    Points: 20,637, Level: 90
    Level completed: 58%, Points required for next Level: 213
    quark's Avatar
    Location
    Canada
    Posts
    479
    Thanks
    25
    Thanked 196 Times in 73 Posts
    P(no oil)=0.30, I think 0.30 should be in there somewhere.

  9. #9
    Points: 5,009, Level: 45
    Level completed: 30%, Points required for next Level: 141

    Posts
    5
    Thanks
    0
    Thanked 0 Times in 0 Posts
    I still did not get it because the first problem identify no oil as 030, but then addt information was given and teh probabilities change. So I thought I would be working from the second set of new probabilities.

  10. #10
    Admin
    Points: 20,637, Level: 90
    Level completed: 58%, Points required for next Level: 213
    quark's Avatar
    Location
    Canada
    Posts
    479
    Thanks
    25
    Thanked 196 Times in 73 Posts

    P(high-quality oil | soil) = p(soil /high quality oil)*p(high quality oil) /[p(soil /high quality oil)*p(high quality oil) + p(soil /medium quality oil)*p(medium quality oil) +p(soil /no oil)*p(no oil)]
    =.20*.50/[.20*.50 + .80*.20 + .20*.30]

    My first post was a general comment regarding Bayes theorem. There are three groups in your problem, so you need to use all three groups.

+ Reply to Thread

           




Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts






Advertise on Talk Stats