Chapter 6, Problem 20P

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8th Edition

Frederick J Gravetter + 1 other

ISBN: 9781133956570

Textbook Problem

A report in 2010 indicates that Americans between the ages of 8 and 18 spend an average of μ = 7.5 hours per day using some sort of electronic device such as smart phones, computers, or tablets. Assume that the distribution of times is normal with a standard deviation of σ = 2.5 hours and find the following values.

**a.**What is the probability of selecting an individual who uses electronic devices more than 12 hours a day?**b.**What proportion of 8- to 18-year-old Americans spend between 5 and 10 hours per day using electronic devices? In symbols.*p*(5 < X < 10) = ?

**a.**

To determine

**To find:** The probability of individual who uses electronic devices more than 12 hours day.

Explanation

**Given info:**

The distribution follows normal distribution with mean 7.5 and standard deviation 2.5 and the individual uses electronic device for more than 12 hours.

**Calculation:**

Calculating the probability that the individual uses electronic device for more than 12 hours is as follows:

The formula for finding the *z* score is,

Substitute 12 for X , 7.5 for

**b.**

To determine

**To find:** The probability of individual who uses electronic devices between 5 to 10 hours a day.

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