Results 1 to 3 of 3

Math Help - Probability

  1. #1
    Member
    Joined
    Jul 2008
    Posts
    212

    Probability

    a) X ~ N(10, 0.25)
    Find P( > 10.25) where n = 10
    Find x such that P( > x) = 0.05 where n = 10

    b) X ~ N(20.2, 4)
    Find P( < 19) where n = 20
    Find x such that P( < x) = 0.85 where n = 20

    If someone could do a) as an example I should be able to do b. Also the are supposed to be capital X's with the hat on top.

    Thanks in advance.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor matheagle's Avatar
    Joined
    Feb 2009
    Posts
    2,763
    Thanks
    5
    You need to standardize the sample mean.

    Z={\bar X-\mu\over \sigma/\sqrt n}\sim N(0,1)

    So, P(\bar X >10.25)= P\biggl(Z> {10.25-10\over .5/\sqrt{10}}\biggr)

    Since Z_{.05}=1.645 the corresponding x value can be solved via 1.645={x-10\over .5/\sqrt {10}}.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Apr 2009
    From
    US
    Posts
    16
    be cearful, if you are saying X ~ N(10, 0.25) =>
    var=0.25 or sd=0.25 ???
    some textbooks use format of X~N(mean, sd), anothers X~N(mean, var).

    solution was provided by matheagle, assuming X~N(mean, var) format.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 10
    Last Post: January 21st 2011, 11:47 AM
  2. Replies: 3
    Last Post: May 29th 2010, 07:29 AM
  3. fundamental in probability & convergence with probability 1
    Posted in the Advanced Statistics Forum
    Replies: 3
    Last Post: February 23rd 2010, 09:58 AM
  4. Replies: 1
    Last Post: February 18th 2010, 01:54 AM
  5. Replies: 3
    Last Post: December 15th 2009, 06:30 AM

Search Tags


/mathhelpforum @mathhelpforum