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Introductory Statistics

Prem S. Mann

Chapter 3

Numerical Descriptive Measures - all with Video Answers

Educators


Section 1

Measures of Central Tendency for Ungrouped Data

01:50

Problem 1

Explain how the value of the median is determined for a data set that contains an odd number of observations and for a data set that contains an even number of observations.

Lucas Finney
Lucas Finney
Numerade Educator
01:42

Problem 2

Briefly explain the meaning of an outlier. Is the mean or the median a better measure of central tendency for a data set that contains outliers? Illustrate with the help of an example.

Lucas Finney
Lucas Finney
Numerade Educator
01:10

Problem 3

Using an example, show how outliers can affect the value of the mean.

Lucas Finney
Lucas Finney
Numerade Educator
02:28

Problem 4

Which of the three measures of central tendency (the mean, the median, and the mode) can be calculated for quantitative data only, and which can be calculated for both quantitative and qualitative data? Illustrate with examples.

Lucas Finney
Lucas Finney
Numerade Educator
00:41

Problem 5

Which of the three measures of central tendency (the mean, the median, and the mode) can assume more than one value for a data set? Give an example of a data set for which this summary measure assumes more than one value.

Lucas Finney
Lucas Finney
Numerade Educator
00:36

Problem 6

it possible for a (quantitative) data set to have no mean, no median, or no mode? Give an example of a data set for which this summary measure does not exist.

Lucas Finney
Lucas Finney
Numerade Educator
02:03

Problem 7

Explain the relationships among the mean, median, and mode for symmetric and skewed histograms. Illustrate these relationships with graphs.

Lucas Finney
Lucas Finney
Numerade Educator
01:09

Problem 8

Prices of cars have a distribution that is skewed to the right with outliers in the right tail. Which of the measures of central tendency is the best to summarize this data set? Explain.

Lucas Finney
Lucas Finney
Numerade Educator
01:27

Problem 9

The following data set belongs to a population:
$\begin{array}{llllllll}5 & -7 & 2 & 0 & -9 & 16 & 10 & 7\end{array}$

Lucas Finney
Lucas Finney
Numerade Educator
01:33

Problem 10

The following data set belongs to a sample:
$\begin{array}{lllll}14 & 18 & -1 & 08 & 8\end{array}$
$-16$

Lucas Finney
Lucas Finney
Numerade Educator
01:54

Problem 11

The following table gives the standard deductions and personal exemptions for persons filing with "single" status on their 2009 state income taxes in a random sample of 10 states. Calculate the mean and median for the data on standard deductions for these states.

Lucas Finney
Lucas Finney
Numerade Educator
01:31

Problem 12

Refer to the data table in Exercise 3.11. Calculate the mean and median for the data on personal exemptions for these states.

Lucas Finney
Lucas Finney
Numerade Educator
02:09

Problem 13

The following data give the 2007 gross domestic product (GDP) in billions of dollars for all 50 states. The data are entered in alphabetic order by state (Bureau of Economic Analysis, June 2005).

Lucas Finney
Lucas Finney
Numerade Educator
01:57

Problem 14

The following data give the 2008 profits (in millions of dollars) of the six Arizona-based companies for the year 2008 (Fortune, May 5,2008 ). The data represent the following companies, respectively:
Freeport-McMoRan Copper \& Gold, Avnet, US Airways Group, Allied Waste Industries, Insight Enterprises, and PetSmart.
$2977.0$
$\begin{array}{lllll}393.1 & 427.0 & 273.6 & 77.8 & 258.7\end{array}$
Find the mean and median for these data. Do these data have a mode?

Lucas Finney
Lucas Finney
Numerade Educator
01:24

Problem 15

The following data give the 2006-07 team salaries for 20 teams of the English Premier League, arguably the best-known soccer league in the world. The salaries are given in the order in which the teams finished during the $2006-07$ season. The salaries are in millions of British pounds (note that the approximate value of 1 British pound was $\$ 1.95$ during the $2006-07$ season, so the team salaries range from $\$ 34.3$ million to $\$ 259$ million). (Source: $B B C$, May $28,2008 .$ ) $\begin{array}{lrlllll}92.3 & 132.8 & 77.6 & 89.7 & 43.8 & 38.4 & 30.7 \\ 29.8 & 36.9 & 36.7 & 43.2 & 38.3 & 62.5 & 36.4 \\ 44.2 & 35.2 & 27.5 & 22.4 & 34.3 & 17.6 & \end{array}$ Find the mean and median for these data.

Lucas Finney
Lucas Finney
Numerade Educator
01:31

Problem 16

The following data give the numbers of car thefts that occurred in a city during the past 12 days.
$\begin{array}{lccccccccccc}6 & 3 & 7 & 11 & 4 & 3 & 8 & 7 & 2 & 6 & 9 & 15\end{array}$
Find the mean, median, and mode.

Lucas Finney
Lucas Finney
Numerade Educator
01:19

Problem 17

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?

Lucas Finney
Lucas Finney
Numerade Educator
01:03

Problem 18

The following table gives the number of major penalties for each of the 15 teams in the Eastern Conference of the National Hockey League during the 2008-09 season (NHL, 2009). A major penalty is subject to 5 minutes in the penalty box for a player.

Lucas Finney
Lucas Finney
Numerade Educator
01:23

Problem 19

Due to antiquated equipment and frequent windstorms, the town of Oak City often suffers power outages. The following data give the numbers of power outages for each of the past 12 months.
$\begin{array}{llllllllll}4 & 5 & 7 & 3 & 2 & 0 & 2 & 3 & 2 & 1 & 2 & 4\end{array}$
Compute the mean, median, and mode for these data.

Lucas Finney
Lucas Finney
Numerade Educator
01:07

Problem 20

A brochure from the department of public safety in a northern state recommends that motorists should carry 12 items (flashlights, blankets, and so forth) in their vehicles for emergency use while driving in winter. The following data give the number of items out of these 12 that were carried in their vehicles by 15 randomly selected motorists.
$\begin{array}{llllllllllllllll}5 & 3 & 7 & 8 & 0 & 1 & 0 & 5 & 1 & 21 & 07 & 6 & 7 & 1 & 19\end{array}$
Find the mean, median, and mode for these data. Are the values of these summary measures population parameters or sample statistics? Explain.

Lucas Finney
Lucas Finney
Numerade Educator
01:04

Problem 21

Nixon Corporation manufactures computer monitors. The following data are the numbers of computer monitors produced at the company for a sample of 10 days.
$\begin{array}{lllllll}24 & 32 & 27 & 23 & 35 & 33 & 29\end{array}$
40
23
28
Calculate the mean, median, and mode for these data.

Lucas Finney
Lucas Finney
Numerade Educator
00:57

Problem 22

The Tri-City School District has instituted a zero-tolerance policy for students carrying any objects that could be used as weapons. The following data give the number of students suspended during each of the past 12 weeks for violating this school policy.
$\begin{array}{llllllll}1 & 59 & 1 & 21 & 17 & 6 & 9 & 1 & 01\end{array}$
$43 \quad 6$
Calculate the mean, median, and mode for these data

Lucas Finney
Lucas Finney
Numerade Educator
02:37

Problem 23

The following data represent the numbers of tornadoes that touched down during 1950 to 1994 in the 12 states that had the most tornadoes during this period (Storm Prediction Center, 2009). The data for these states are given in the following order: CO, FL, IA, IL, KS, LA, MO, MS, NE, OK, SD, TX.
$\begin{array}{llllllllllll}1113 & 2009 & 1374 & 1137 & 2110 & 1086 & 1166 & 1039 & 1673 & 2300 & 1139 & 5490\end{array}$
a. Calculate the mean and median for these data.
b. Identify the outlier in this data set. Drop the outlier and recalculate the mean and median. Which of these two summary measures changes by a larger amount when you drop the outlier?
c. Which is the better summary measure for these data, the mean or the median? Explain.

Lucas Finney
Lucas Finney
Numerade Educator
02:05

Problem 24

The following data set lists the number of women from each of 10 different countries who were on the Rolex Women's World Golf Rankings Top 25 list as of March 31,2009 . The data, entered in that order, are for the following countries: Australia, Brazil, England, Japan, Korea, Mexico, Norway, Sweden, Taiwan, and United States.
$\begin{array}{lllllllll}2 & 1 & 1 & 2 & 9 & 1 & 1 & 2 & 2 & 4\end{array}$
a. Calculate the mean and median for these data.
b. Identify the outlier in this data set. Drop the outlier and recalculate the mean and median. Which of these two summary measures changes by a larger amount when you drop the outlier?
c. Which is the better summary measure for these data, the mean or the median? Explain.

Lucas Finney
Lucas Finney
Numerade Educator
00:42

Problem 25

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:
$\left.n_{1}=10, n_{2}=8, \bar{x}_{1}=\$ 140, \bar{x}_{2}=\$ 160 .\right)$

Lucas Finney
Lucas Finney
Numerade Educator
02:38

Problem 26

Twenty business majors and 18 economics majors go bowling. Each student bowls one game. The scorekeeper announces that the mean score for the 18 economics majors is 144 and the mean score for the entire group of 38 students is 150 . Find the mean score for the 20 business majors.

Matthew Wagner
Matthew Wagner
Numerade Educator
00:43

Problem 27

For any data, the sum of all values is equal to the product of the sample size and mean; that is, $\Sigma x=n \bar{x}$. Suppose the average amount of money spent on shopping by 10 persons during a given week is $\$ 105.50$. Find the total amount of money spent on shopping by these 10 persons.

Lucas Finney
Lucas Finney
Numerade Educator
00:52

Problem 28

The mean 2009 income for five families was $\$ 99,520$. What was the total 2009 income of these
five families?

Lucas Finney
Lucas Finney
Numerade Educator
01:22

Problem 29

The mean age of six persons is 46 years. The ages of five of these six persons are $57,39,44,51$, and 37 years, respectively. Find the age of the sixth person.

Lucas Finney
Lucas Finney
Numerade Educator
02:45

Problem 30

Seven airline passengers in economy class on the same flight paid an average of $\$ 361$ per ticket. Because the tickets were purchased at different times and from different sources, the prices varied. The first five passengers paid $\$ 420, \$ 210, \$ 333, \$ 695$, and $\$ 485$. The sixth and seventh tickets were purchased by a couple who paid identical fares. What price did each of them pay?

Vipender Yadav
Vipender Yadav
Numerade Educator
01:37

Problem 31

Consider the following two data sets. $\begin{array}{llllrl}\text { Data Set I: } & 12 & 25 & 37 & 8 & 41 \\ \text { Data Set II: } & 19 & 32 & 44 & 15 & 48\end{array}$
Notice that each value of the second data set is obtained by adding 7 to the corresponding value of the first data set. Calculate the mean for each of these two data sets. Comment on the relationship between the two means.

MD
Maria Donnelly
Numerade Educator
01:37

Problem 32

Consider the following two data sets. $\begin{array}{llrlrl}\text { Data Set I: } & 4 & 8 & 15 & 9 & 11 \\ \text { Data Set II: } & 8 & 16 & 30 & 18 & 22\end{array}$
Notice that each value of the second data set is obtained by multiplying the corresponding value of the first data set by 2. Calculate the mean for each of these two data sets. Comment on the relationship between the two means.

MD
Maria Donnelly
Numerade Educator
05:56

Problem 33

The trimmed mean is calculated by dropping a certain percentage of values from each end of a ranked data set. The trimmed mean is especially useful as a measure of central tendency when a data set contains a few outliers at each end. Suppose the following data give the ages (in years) of 10 employees of a company:
$\begin{array}{llllllll}47 & 53 & 38 & 26 & 39 & 49 & 19 & 67 & 31\end{array}$
23
To calculate the $10 \%$ trimmed mean, first rank these data values in increasing order; then drop $10 \%$ of the smallest values and $10 \%$ of the largest values. The mean of the remaining $80 \%$ of the values will give the $10 \%$ trimmed mean. Note that this data set contains 10 values, and $10 \%$ of 10 is $1 .$ Thus, if we drop the smallest value and the largest value from this data set, the mean of the remaining 8 values will be called the $10 \%$ trimmed mean. Calculate the $10 \%$ trimmed mean for this data set.

Pammi Eswari
Pammi Eswari
Numerade Educator
00:37

Problem 34

The following data give the prices (in thousands of dollars) of 20 houses sold recently in a city.
$\begin{array}{llllllllll}184 & 297 & 365 & 309 & 245 & 387 & 369 & 438 & 195 & 390 \\ 323 & 578 & 410 & 679 & 307 & 271 & 457 & 795 & 259 & 590\end{array}$ Find the $20 \%$ trimmed mean for this data set.

Ahmad Reda
Ahmad Reda
Numerade Educator
04:14

Problem 35

In some applications, certain values in a data set may be considered more important than others. For example, to determine students' grades in a course, an instructor may assign a weight to the final exam that is twice as much as that to each of the other exams. In such cases, it is more appropriate to use the weighted mean. In general, for a sequence of $n$ data values $x_{1}, x_{2}, \ldots, x_{n}$ that are assigned weights $w_{1}$, $w_{2}, \ldots, w_{n}$, respectively, the weighted mean is found by the formula
$$
\text { Weighted mean }=\frac{\sum x w}{\sum w}
$$
where $\Sigma x w$ is obtained by multiplying each data value by its weight and then adding the products. Suppose an instructor gives two exams and a final, assigning the final exam a weight twice that of each of the other exams. Find the weighted mean for a student who scores 73 and 67 on the first two exams and 85 on the final. (Hint: Here, $x_{1}=73, x_{2}=67, x_{3}=85, w_{1}=w_{2}=1$, and $w_{3}=2 .$ )

Joshua Argo
Joshua Argo
Numerade Educator
01:28

Problem 36

When studying phenomena such as inflation or population changes that involve periodic increases or decreases, the geometric mean is used to find the average change over the entire period under study. To calculate the geometric mean of a sequence of $n$ values $x_{1}, x_{2}, \ldots, x_{n}$, we multiply them together and then find the $n$ th root of this product. Thus
$$
\text { Geometric mean }=\sqrt[n]{x_{1} \cdot x_{2} \cdot x_{3} \cdot \ldots \cdot x_{n}}
$$
Suppose that the inflation rates for the last five years are $4 \%, 3 \%, 5 \%, 6 \%$, and $8 \%$, respectively. Thus at the end of the first year, the price index will be $1.04$ times the price index at the beginning of the year, and so on. Find the mean rate of inflation over the 5 -year period by finding the geometric mean of the data set $1.04,1.03,1.05,1.06$, and $1.08 .$ (Hint: Here, $n=5, x_{1}=1.04, x_{2}=1.03$, and so on. Use the $x^{1 / n}$ key on your calculator to find the fifth root. Note that the mean inflation rate will be obtained by subtracting 1 from the geometric mean.)

Jerrah Biggerstaff
Jerrah Biggerstaff
Numerade Educator