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Math Help - z-score

  1. #1
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    z-score

    First I would like to say that im surprised i havent found a forum like this until now, im very excited to help others with their math problems (the most i can atleast) as much as i am excited to get other peoples help I would really appreciate help on these questions; I have posted the questions i am doing and the answers I have, if anyone can confirm/deny how correct I am and help accordingly that would be extremely appreciated.

    Just doing questions in my text book for my econ statistics class in preparation for the midterm and for some reason am stuck on this question. From what i understand the best "interval" system to use is a Z-score, but with the information given how do i apply it?

    1.

    z = (X - U)/ O


    x = raw score (which would be what in this case?)
    U = mean
    O = standard deviation

    I have the standard deviation and mean (12.02 and 4.25) but whats the raw score? and how do i expect the distribution to be?

    Question:

    2.76 Blogs for Fortune 500 firms. Refer to the Journal of Relationship Marketing (Vol. 7, 2008) study of the preva- lence of blogs and forums at Fortune 500 firms with both English and Chinese Web sites, Exercise 2.9 (p. 40). In a sample of firms that provide blogs and forums as market- ing tools, the mean number of blogs/forums per site was 4.25, with a standard deviation of 12.02.
    a. Provide an interval that is likely to contain the number of blogs/forums per site for at least 75% of the Fortune 500 firms in the sample.
    b. Do you expect the distribution of the number of blogs/forums to be symmetric, skewed right, or skewed left? Explain.



    2.9 Blogs for Fortune 500 firms. Web site communication through blogs and forums is becoming a key marketing tool for companies. The Journal of Relationship Marketing (Vol. 7, 2008) investigated the prevalence of blogs and fo- rums at Fortune 500 firms with both English and Chinese Web sites. Of the firms that provided blogs/forums as a marketing tool, the accompanying table gives a breakdown on the entity responsible for creating the blogs/forums. Use a graphical method to describe the data summarized in the table. Interpret the graph.

    Blog/forum Percentage
    Created by company 38.5
    Created by employees 34.6
    Created by third party 11.5
    Creator not identified 15.4
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  2. #2
    MHF Contributor

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    Quote Originally Posted by noid View Post
    First I would like to say that im surprised i havent found a forum like this until now, im very excited to help others with their math problems (the most i can atleast) as much as i am excited to get other peoples help I would really appreciate help on these questions; I have posted the questions i am doing and the answers I have, if anyone can confirm/deny how correct I am and help accordingly that would be extremely appreciated.

    Just doing questions in my text book for my econ statistics class in preparation for the midterm and for some reason am stuck on this question. From what i understand the best "interval" system to use is a Z-score, but with the information given how do i apply it?

    1.

    z = (X - U)/ O


    x = raw score (which would be what in this case?)
    U = mean
    O = standard deviation

    I have the standard deviation and mean (12.02 and 4.25) but whats the raw score? and how do i expect the distribution to be?

    Question:

    2.76 Blogs for Fortune 500 firms. Refer to the Journal of Relationship Marketing (Vol. 7, 2008) study of the preva- lence of blogs and forums at Fortune 500 firms with both English and Chinese Web sites, Exercise 2.9 (p. 40). In a sample of firms that provide blogs and forums as market- ing tools, the mean number of blogs/forums per site was 4.25, with a standard deviation of 12.02.
    a. Provide an interval that is likely to contain the number of blogs/forums per site for at least 75% of the Fortune 500 firms in the sample.
    You want P(\frac{x- 4.25}{12.02})\ge 0.75. Look up "z" corresponding to P(z)= 0.75 in a table of the normal distribution. Then you want \frac{x- 4.25}{12.02}\ge z or x\ge 12.02z+ 4.25.

    b. Do you expect the distribution of the number of blogs/forums to be symmetric, skewed right, or skewed left? Explain.



    2.9 Blogs for Fortune 500 firms. Web site communication through blogs and forums is becoming a key marketing tool for companies. The Journal of Relationship Marketing (Vol. 7, 2008) investigated the prevalence of blogs and fo- rums at Fortune 500 firms with both English and Chinese Web sites. Of the firms that provided blogs/forums as a marketing tool, the accompanying table gives a breakdown on the entity responsible for creating the blogs/forums. Use a graphical method to describe the data summarized in the table. Interpret the graph.

    Blog/forum Percentage
    Created by company 38.5
    Created by employees 34.6
    Created by third party 11.5
    Creator not identified 15.4
    Last edited by mr fantastic; October 11th 2010 at 03:04 PM. Reason: Fixed quote tags and a maths tag.
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  3. #3
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    Joined
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    P(z) = 0.75 corresponds to .7734

    Should i be using this corresponding value to substitute for z in x\ge 12.02z+ 4.25. or should i be using the original .75 (75%)? I assume .7734.

    From what i understand, that would give me a z-scrore (and interval) of plus/minus .7734 and a raw score (z) of 13.55.

    Could I then be said for part b) that it would be symmetrical?
    Last edited by mr fantastic; October 11th 2010 at 03:06 PM. Reason: Too annoying to fix quote tags here. Quote deleted.
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