Results 1 to 6 of 6

Math Help - Probability - Normal Distribution

  1. #1
    Member
    Joined
    Jan 2010
    Posts
    77

    Probability - Normal Distribution

    Given that X~N(-3,5^2), calculate the probability.

    P(|X|>5)

    What I did was transform it and then put calculate the probability with my graphing calculator and got 0.0547992894.
    Then, I multiplied it by 2 to get 0.1096.
    However, the answer in the book is 0.3994.
    Can someone else please do this question and tell me what you get?
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by bhuang View Post
    Given that X~N(-3,5^2), calculate the probability.

    P(|X|>5)

    What I did was transform it and then put calculate the probability with my graphing calculator and got 0.0547992894.
    Then, I multiplied it by 2 to get 0.1096.
    However, the answer in the book is 0.3994.
    Can someone else please do this question and tell me what you get?
    You require Pr(X > 5) + Pr(X < -5). If you draw a diagram showing the required area under the curve it will be clear that your use of symmetry is not valid.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Member
    Joined
    Jan 2010
    Posts
    77

    Probability - Normal Distribution

    I am finding Pr(X > 5) + Pr(X < -5). And I transformed it, so the normal distribution would have a mean of 0 and standard deviation of 1. But the answer is still different from that of the book's.
    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 bhuang View Post
    I am finding Pr(X > 5) + Pr(X < -5). And I transformed it, so the normal distribution would have a mean of 0 and standard deviation of 1. But the answer is still different from that of the book's.
    Please show the details of your calculation.
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Member
    Joined
    Jan 2010
    Posts
    77

    Probability - Normal Distribution

    I know what I did wrong now.
    I figured that because I transformed it, then |X|>5 would be symmetrical, but it isn't the case because when I transform it, the two random variables are different. Since I figured it was symmetrical, I multiplied the transformed random variables by 2. But the right way to do it is to add the probabilities of each distinct random variable.
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by bhuang View Post
    I know what I did wrong now.
    I figured that because I transformed it, then |X|>5 would be symmetrical, but it isn't the case because when I transform it, the two random variables are different. Since I figured it was symmetrical, I multiplied the transformed random variables by 2. [snip]
    Aha. So you re-read post #2 ....
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. probability normal distribution
    Posted in the Advanced Statistics Forum
    Replies: 1
    Last Post: August 16th 2010, 05:57 PM
  2. by a normal probability distribution?
    Posted in the Advanced Statistics Forum
    Replies: 0
    Last Post: October 2nd 2009, 09:20 PM
  3. normal distribution probability
    Posted in the Advanced Statistics Forum
    Replies: 0
    Last Post: September 10th 2009, 06:58 PM
  4. probability...normal distribution
    Posted in the Statistics Forum
    Replies: 2
    Last Post: May 5th 2008, 12:04 PM
  5. Normal Distribution, Std. Dev., & Probability
    Posted in the Advanced Statistics Forum
    Replies: 3
    Last Post: April 29th 2008, 03:48 AM

Search Tags


/mathhelpforum @mathhelpforum