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Math Help - Indepedant events.

  1. #1
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    Independant events.

    I hope this isn't too long winded, I have most the answers, just need a check and some help on the last part.

    Laser surgery to fix short-sightedness is becoming more popular. However, for some people, a second procedure is necessary. The following table lists the joint probability of needing a second procedure and whether the patient has a corrective lens with a factor (dioptre) of minus 8 or less.

    This is supposed to be a table!

    __________________ Vision corrective factor > -8, Vision corrective factor <= -8

    1st procedure successful ~~~~~~___________0.66 ~~~~~~___________________0.15


    2nd procedure required ~~~~~~____________0.05 ~~~~~~___________________0.14




    a) Find the probability that a second procedure is required.

    This is simply 0.05+0.14 = 0.19



    b) Determine the probability that someone whose corrective lens factor is minus 8 or less does not require a second procedure.

    This is 0.66+0.15+0.14 = 0.95


    c) Are the events independent? Explain your answer.

    I think the answer is yes, but I don't know how to explain
    Last edited by Bushy; April 7th 2010 at 03:18 AM. Reason: bad spelling
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  2. #2
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    Quote Originally Posted by Bushy View Post
    I hope this isn't too long winded, I have most the answers, just need a check and some help on the last part.

    Laser surgery to fix short-sightedness is becoming more popular. However, for some people, a second procedure is necessary. The following table lists the joint probability of needing a second procedure and whether the patient has a corrective lens with a factor (dioptre) of minus 8 or less.

    This is supposed to be a table!

    __________________ Vision corrective factor > -8, Vision corrective factor <= -8

    1st procedure successful ~~~~~~___________0.66 ~~~~~~___________________0.15


    2nd procedure required ~~~~~~____________0.05 ~~~~~~___________________0.14




    a) Find the probability that a second procedure is required.

    This is simply 0.05+0.14 = 0.19



    b) Determine the probability that someone whose corrective lens factor is minus 8 or less does not require a second procedure.

    This is 0.66+0.15+0.14 = 0.95


    c) Are the events independent? Explain your answer.

    I think the answer is yes, but I don't know how to explain
    (b) Pr(2nd procedure NOT required | corrective lens factor < -8) = 0.15/(0.15 + 0.14).

    (c) Does Pr(2nd procedure NOT required | corrective lens factor < -8) = Pr(2nd procedure NOT required) ....?
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