Do people of different age groups differ in their response to email messages? A survey by the Center for the Digital Future of the University of Southern California (data extracted from A. Mindlin, "Older E-mail Users Favor Fast Replies," The New York Times, July 14, 2008, p. B3) reported that 70.7% of users over 70 years of age believe that email messages should be answered quickly, as compared to 53.6% of users 12 to 50 years old. Suppose that the survey was based on 1,000 users over 70 years of age and 1,000 users 12 to 50 years old. The following table summarizes the results:

a. Give an example of a simple event.
b. Give an example of a joint event.
c. What is the complement of a respondent who answers quickly?
d. Why is a respondent who answers quickly and is over 70 years old a joint event?

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AGE OF RESPONDENTS ANSWERS QUICKLY 12-50 Over 70 Total 536 464 1,000 Yes No Total 707 293 1,000 1,243 757 2,000