Results 1 to 2 of 2

Math Help - Confidence level

  1. #1
    Newbie
    Joined
    May 2009
    Posts
    2

    Exclamation Confidence level

    The director of a museum would like to know what fraction of the museum associates make purchases through the gift shop catalog

    A) If no preliminary study is done, how large a sample must be taken if the director is to say with 90% confidence that the sample estimate is within 2% of the population proportion?

    B) A preliminary study showed that out of 60 associates 12 have used the gift shop catalog, what size sample does the director need in order to say with 90% confidence that the sample estimate is within 2% of the population proportion??

    Any guidance would be much appreciated, not exactly sure how to start with this one, thanks in advance for any help
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Super Member Random Variable's Avatar
    Joined
    May 2009
    Posts
    959
    Thanks
    3
    A 90% confidence interval for p is  \hat{p} \pm z_{0.05} \sqrt { \frac {\hat{p}(1-\hat{p)}}{n}}

    So you want  z_{0.05} \sqrt { \frac {\hat{p}(1-\hat{p})}{n}} = 0.02

    You don't know  \hat{p} in part (A), (in part (B) \hat{p} is 12/60) but you can use the fact that  \hat{p}(1-\hat{p}) \le \frac {1}{4}

    Now all you have to do is solve for n.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Find Confidence Level of Coefficients
    Posted in the Advanced Statistics Forum
    Replies: 0
    Last Post: March 9th 2011, 12:08 PM
  2. Probablity and Confidence Level Question
    Posted in the Statistics Forum
    Replies: 4
    Last Post: December 4th 2009, 12:54 PM
  3. confidence level and confidence interval?
    Posted in the Advanced Statistics Forum
    Replies: 2
    Last Post: July 12th 2009, 07:59 AM
  4. confidence level
    Posted in the Advanced Statistics Forum
    Replies: 9
    Last Post: July 2nd 2009, 05:51 AM
  5. Confidence level
    Posted in the Advanced Statistics Forum
    Replies: 3
    Last Post: May 30th 2009, 04:31 AM

Search Tags


/mathhelpforum @mathhelpforum