Have you had a business presentation disturbed by a ringing cellphone? In a poll

Question

Have you had a business presentation disturbed by a ringing cellphone? In a poll of 326 business men and women, 303 answered this question “yes” and only 23 answered “no” (“You Say,” Presentations: Technology and Techniques for Effective Communication, January 2003.)
a. Construct a 95% confidence interval for the population proportion of business men and women who have their presentations distributed by cellphones.
b. Interpret the interval constructed in (a).
c. To conduct a follow-up study that would provide 95% confidence level that the point estimate is correct to within 0.04 of the population proportion, how large a sample size is required?
d. To conduct a follow-up study that would provide 99% confidence level that the point estimate is correct to within 0.04 of the population proportion, how large a sample size is required?

Explanation / Answer

a)

b)

above interval gives 95% confidence to contain true proportion   of business men and women who have their presentations distributed by cellphones.

c)

d)

                                                                                           x                    =   303 sample size n                    = 326 sample proportion     p x/n= 0.9294 std error       =Se            =(p*(1-p)/n) = 0.0142 for 95 % CI value of z= 1.9600 margin of error E=z*std error                            = 0.028 lower confidence bound=sample proportion-margin of error 0.902 Upper confidence bound=sample proportion+margin of error 0.957

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