Concept explainers
Downloading “apps” to your cell phone. 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 next table gives the probability distribution for x, 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.)
Number of “Apps” Used, x | p(x) | ||
0 | .17 | ||
1 | .10 | ||
2 | .11 | ||
3 | .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 |
- a. Show that the properties of a probability distribution for a discrete random variable are satisfied.
- b. Find P (x ≥ 10).
- c. Find the mean and variance of x.
- d. Give an interval that will contain the value of x with a probability of at least .75.
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