Chapter 4, Problem 4.173ACB

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

1. a. Show that the properties of a probability distribution for a discrete random variable are satisfied.
2. b. Find P (x ≥ 10).
3. c. Find the mean and variance of x.
4. d. Give an interval that will contain the value of x with a probability of at least .75.