Chapter 3: Problem 89
Explain the concept of the percentile rank for an observation of a data set.
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Chapter 3: Problem 89
Explain the concept of the percentile rank for an observation of a data set.
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Refer to Exercise \(3.115\). Suppose the times taken to learn the basics of this word processor by all students have a bell-shaped distribution with a mean of 200 minutes and a standard deviation of 20 minutes. a. Using the empirical rule, find the percentage of students who will learn the basics of this word processor in i. 180 to 220 minutes ii. 160 to 240 minutes "b. Using the empirical rule, find the interval that contains the time taken by \(99.7 \%\) of all students to learn this word processor.
One property of the mean is that if we know the means and sample sizes of two (or more) data sets, we can calculate the combined mean of both (or all) data sets. The combined mean for two data sets is calculated by using the formula $$ \text { Combined mean }=\bar{x}=\frac{n_{1} \bar{x}_{1}+n_{2} \bar{x}_{2}}{n_{1}+n_{2}} $$ where \(n_{1}\) and \(n_{2}\) are the sample sizes of the two data sets and \(\bar{x}_{1}\) and \(\bar{x}_{2}\) are the means of the two data sets, respectively. Suppose a sample of 10 statistics books gave a mean price of \(\$ 140\) and a sample of 8 mathematics books gave a mean price of \(\$ 160\). Find the combined mean. (Hint: For this example: \(\left.n_{1}=10, n_{2}=8, \bar{x}_{1}=\$ 140, \bar{x}_{2}=\$ 160 .\right)\)
How much does the typical American family spend to go away on vacation each year? Twenty-five randomly selected households reported the following vacation expenditures (rounded to the nearest hundred dollars) during the past year:
The following data give the revenues (in millions of dollars) for the last available fiscal year for a sample of six charitable organizations for serious diseases (Charity Navigator, 2009). The values are, listed in order, for the Alzheimer's Association, the American Cancer Society, the American Diabetes Association, the American Heart Association, the American Lung Association, and the Cystic Fibrosis Foundation. \(\begin{array}{llllll}952 & 1129 & 231 & 668 & 49 & 149\end{array}\) Compute the mean and median. Do these data have a mode? Why or why not?
The mean 2009 income for five families was \(\$ 99,520\). What was the total 2009 income of these five families?
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