Use Theorem 4.4 to calculate the variance of the probability distribution in Exercise 4.12. Verify that your result agrees with Exercise 4.12.

Data from Exercise 4.12

According to an August, 2011 survey by the Pew Internet & American Life Project, nearly 40% of adult cell phone owners have downloaded an application (“app”) to their cell phone. The accompanying table gives the probability distribution for Y, the number of “apps” used at least once a week by cell phone owners who have downloaded an “app” to their phone. (The probabilities in the table are based on information from the Pew Internet & American Life Project survey.)

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Number of "apps" used, y .17 1 .10 .11 .11 4 .10 5 .10 6 .07 7 .05 8. .03 9 .02 10 .02 11 .02 12 .02 13 .02 14 .01 15 .01 16 .01 17 .01 18 .01 19 .005 20 .005