W4002-Set up a 95% confidence interval estimate of the population average number of shares traded for......?

The following table is a random sample of 18 stocks traded on the New York Stock Exchange as reported in the Cincinnati Enquirer (May 18, 1999). For each stock, the table lists the company name and the number of shares that traded hands on May 17, 1999.





Company Shares


AllenTel 408700


Banctec 29500


CDI 32500


CTS 36700


Dover 169100


Fluor 332000


Grace 237700


Hartmx 49700


KCS 110300


LizClab 219400


NuvPP 50700


Presly 133500


StJude 163500


Scripps 27900


SunEng 63400


Thai 67200


Tyson 161800


YorkIn 120000





(a) Set up a 95% confidence interval estimate of the population average number of shares traded for a company on the New York Stock Exchange on May 17, 1999.





(b) What sample size is needed if you want to be 95% confident of being correct to within :t:20,000 shares?





(c) If you were to perform this study today, do you think that your answer to (b) is valid? Explain.





THANKS!

W4002-Set up a 95% confidence interval estimate of the population average number of shares traded for......?
I computed mean m=134088.89 and


standard deviation s=105878.03.


I know that the statististic


T=sqrt(n) * (X-134088.89)/105878.03


has a Student t-distribtuion with 18-1=17 degrees of freedom.


The table of the Student-t distribution gives the solution c


of the equation. P(T%26gt;=c )-P(T%26lt;=-c) = 0.95, c =2.11


So -2.11 %26lt;sqrt(n) * (X-134088.89)/105878.03%26lt;2.11


gives the interval.


I leave the rest to you!