Question

Have you had a business presentation disturbed by a ringing cell phone? 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, 18). Round p-hat to 4 decimal places! Which of the following represents a 90% confidence interval for the population proportion of business men and women who have had their presentations disturbed by cell phones?

Answer 1

n = number of sample = 326

X = number of success = 303

p-hat

Zc = 1.645

Using following procedure we found z value

C= confidence interval = 0.90

Using excel =NORMSINV(0.95) =1.645 or you can use Z table to find z value .

( 0.9061 ,0.9528 )

We are 90% confident that population proportion of business men and women who have had their presentations disturbed by cell phones is lies between 0.9061 to 0.9528.