Question

8. Marginal, joint, and conditional probabilities based on a crosstabulation Aa Aa E Surveys conducted for the Pew Internet & American Life Project suggest that communication pattems vary across three groups of teenagers: social networkers, content creators, and multichannel teens (teens who use the Internet instant messaging, text-messaging cell phones, and social networks). In one survey, Internet-using teenagers were asked how often they send e-mail to friends. Their responses are summarized in the following (incomplete) crosstabulation. Separate tabulations are provided for social networkers (teens who have a profile on a social network site such as Facebook or Instagram) and for teens who are not social networkers. Fill in the empty cells in the following crosstabulation: E-mails Every Day Does Not E-mail Every Day Total 104 493 Social networker Not a social networker Total 365 8.86 - - Let S N E O the event the Internet-using teen is a social networker, the event the Internet-using teen is not a social networker, the event the Internet-using teen sends e-mail to friends every day, and the event the Internet-using teen does not send e-mail to friends every day. Consider this experiment: An Internet using teenager is randomly selected and surveyed. The teen is categorized as a social networker or not a social networker and as someone who sends e-mail to friends every day or someone who does not What is the probability that the randomly selected Internet-using teenager does not send e-mail to friends every day? O 0.44 O 0.85 015

Answer 1

The empty cells are filled in the following table :

	E-mails every day	Does not E-mails every day	Total
Social networker	104	493-104 = 389	493
Not a Social Networker	393-365 =28	365	886-493=393
Total	104+28 = 132	389+365 =754	886

Now,

The probability that the randomly selected Internet using teenager does not send e-mail to friend everyday = P(O)

Number of the Internet using teenager does not send e-mail to friend everyday P(O) = Total number of Internet using teenagers

754 = as = 0.8510~0.85

Answer: 0.85