Results 1 to 5 of 5

Math Help - Conditional probability.

  1. #1
    Newbie
    Joined
    Mar 2009
    Posts
    14

    Conditional probability.

    Hi,

    I have a test tomorrow and I am really struggling with a question:

    Suppose that among 100,000 women with negative mammograms, 20 will get breast cancer and that 1 woman in 10 with a positive mammogram will get breast cancer. Let A denote positive mammograms and B breast cancer. Find:

    1. p(b|a(compliment))

    2. p(b|a)

    3. suppose that 7% of the general female population will have a positive mammogram. Find the probability of developing breast cancer among this female population.


    I think i understand 1. and 2., would the first part just be 20/100,000 and would part 2 just be 1/10?

    however i really don't get the last part?

    Thanks
    Last edited by mr fantastic; May 20th 2011 at 04:50 AM. Reason: Title.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Joined
    Nov 2008
    From
    France
    Posts
    1,458
    Hi

    OK for 1. and 2.

    For 3.
    p(B) = p(B \cap A) + p(B \cap \overline{A})

    p(B) = p(B|A) p(A) + p(B|\overline{A}) p(\overline{A})
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Mar 2009
    Posts
    14
    hi,

    How does the 7% come in to the answer?


    is the answer 0.00719?

    thanks
    Last edited by mr fantastic; March 3rd 2009 at 07:00 PM. Reason: Merged posts
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by bolton_boy View Post
    [snip]
    Suppose that among 100,000 women with negative mammograms, 20 will get breast cancer and that 1 woman in 10 with a positive mammogram will get breast cancer. Let A denote positive mammograms and B breast cancer. Find:

    [snip]

    3. suppose that 7% of the general female population will have a positive mammogram. Find the probability of developing breast cancer among this female population.

    [snip]
    Quote Originally Posted by running-gag View Post
    Hi

    OK for 1. and 2.

    For 3.
    p(B) = p(B \cap A) + p(B \cap \overline{A})

    p(B) = p(B|A) p(A) + p(B|\overline{A}) p(\overline{A})
    I think Q3 only requires \Pr(B \cap A) = \Pr(B \, | \, A) \Pr(A) = \, ....
    Follow Math Help Forum on Facebook and Google+

  5. #5
    MHF Contributor
    Joined
    Nov 2008
    From
    France
    Posts
    1,458
    Quote Originally Posted by mr fantastic View Post
    I think Q3 only requires \Pr(B \cap A) = \Pr(B \, | \, A) \Pr(A) = \, ....
    Exact ... sorry
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 0
    Last Post: July 22nd 2011, 02:39 AM
  2. Conditional Probability using the Law of Total Probability
    Posted in the Advanced Statistics Forum
    Replies: 1
    Last Post: October 7th 2010, 04:01 AM
  3. Conditional Probability
    Posted in the Statistics Forum
    Replies: 3
    Last Post: December 16th 2009, 07:27 PM
  4. Continuous probability - conditional probability
    Posted in the Statistics Forum
    Replies: 1
    Last Post: October 1st 2009, 02:21 AM
  5. Conditional Probability #2
    Posted in the Statistics Forum
    Replies: 2
    Last Post: April 23rd 2009, 08:07 AM

Search Tags


/mathhelpforum @mathhelpforum