Results 1 to 3 of 3

Math Help - Discrete Random Variable Help

  1. #1
    Newbie
    Joined
    Nov 2010
    Posts
    9

    Discrete Random Variable Help

    Not sure why I'm getting the wrong answer for this question:
    A box contains 5 salt shakers and 3 pepper shakers, each inside a plain cardboard container. If X is the number of containers opened by a person (who does not know the number of salt shakers in the box) searching for a salt shaker, make a table for the probability distribution for X.

    The answer:
    X | Pr[X=x]
    1 5/8
    2 15/56
    3 5/56
    4 1/56

    Can someone please explain why the answer is the way it is?

    Thanks
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor

    Joined
    Aug 2006
    Posts
    18,617
    Thanks
    1581
    Awards
    1
    P(X=3)=P(pps)=\frac{3}{8}\frac{2}{7}\frac{5}{6}=\f  rac{5}{56}
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Super Member
    Joined
    Jul 2009
    Posts
    593
    Thanks
    4
    First, do you understand what the Random Variable X is? It is "Person opens a salt shaker on the X'th try". So the probability he gets it on the first try is indeed 5/8. The probability that he gets it on the second try is the same as the probability he didn't get it on the first try (3/8) times the probability that he opens it on the second try (5/7). And so on. This is a geometric series (that you'll eventually get to), and is used to model "What is the probability it takes X tries for a success" type problems.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. PGF of Discrete Random Variable
    Posted in the Advanced Statistics Forum
    Replies: 3
    Last Post: March 12th 2010, 04:21 PM
  2. Replies: 3
    Last Post: January 13th 2010, 10:44 AM
  3. Example of a discrete random variable
    Posted in the Statistics Forum
    Replies: 1
    Last Post: November 16th 2008, 10:49 PM
  4. Discrete random variable help!
    Posted in the Advanced Statistics Forum
    Replies: 1
    Last Post: July 18th 2008, 11:10 PM
  5. discrete random variable
    Posted in the Advanced Statistics Forum
    Replies: 4
    Last Post: December 23rd 2007, 01:13 AM

Search Tags


/mathhelpforum @mathhelpforum