Practice Problems for Exam 1

ST 311
Topics covered on Exam 1: Chapters 1-7 in text.
This material is covered in webassign homework assignments 1 through 4 and worksheets 1-7.
Exam information: materials allowed: calculator (no laptops or tablets), one 8 "# x 11 sheet (2 sided)with
notes, definitions, formulas, etc. Normal table will be provided with the exam.
Important Note: Most of the questions on this sample exam are in a multiple choice format, but some
questions are not. The questions on the exam will be multiple choice; you will use a scantron sheet to
indicate your answers.
WARNING! The problems below may not cover all topics for which you are responsible on exam 1.
Answers are at the end of the document.
The heights of American men aged 18 to 24 can be described by a Normal model with mean 68 inches and
standard deviation 2.5 inches. Half of all young men are shorter than
a) 65.5 inches b) 68 inches c) 70.5 inches d) can't tell because the median height is not given
Use the information in Problem 1 and the 68-95-99.7 rule to determine the percentage of young men that are
taller than 6' 1".
The grade point averages (GPA) of 7 randomly chosen students in a statistics class are
3.14 2.37 2.94 3.60 1.70 4.00 1.85
Find these statistics:
a) mean
b) median and quartiles
c) range and IQR
Refer to the information given in the previous problem. If  ÐC3  CÑ# œ %Þ&", what is the standard
A standardized test designed to measure math anxiety has a mean of 100 and a standard deviation
of 10 in the population of first year college students. Which of the following observations would
you suspect is an outlier?
a) 150 b) 100 c) 90 d) 125 e) 87
A clerk entering salary data into a company spreadsheet accidentally put an extra “0” in the boss's salary,
listing it as $2,000,000 instead of $200,000. Explain how this will affect these summary statistics for the
company payroll:
a) measures of center: mean and median
b) measures of spread: range, IQR, and standard deviation
ST 311
Practice Problems Exam 1
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The distribution represented by the histogram below is:
a) skewed to the right.
b) skewed to the left.
c) symmetric.
d) normal.
Twenty-seven applicants interested in working for the Food Stamp program took an examination designed to
measure their aptitude for social work. The following test scores were obtained:
79, 93, 84, 86, 77, 63, 46, 97, 87, 88, 87, 92, 68, 72, 86, 98, 81, 70, 66, 98, 59, 76, 68, 91, 94, 85, 88.
a. Find U" .
b. Construct a boxplot for these observations. Do you observe any outliers?
A manufacturer of television sets has found that for the sets they produce, the lengths of time until the first
repair can be described by a normal model with a mean of 4.5 years and a standard deviation of 1.5 years. If
the manufacturer sets the warrantee so that only 10.2% of the 1st repairs are covered by the warrantee, how
long should the warrantee last?
10. Suppose the amount of tar in cigarettes is described by a normal model with a mean of 3.5 mg and a standard
deviation of 0.5 mg.
a. What proportion of cigarettes have a tar content that exceeds 4.25 mg?
b. In order to advertise as a low tar brand, a manufacturer must prove that their tar content is below the
25th percentile of the tar content distribution. Find the 25th percentile of the distribution of tar amounts.
11. Has the percentage of young girls drinking milk changed over time? The following table is consistent with
the results from “Beverage Choices of Young Females: Changes and Impact on Nutrient Intakes” (Shanthy
A. Bowman, Journal of the American Dietetic Association, 102(9), pp. 1234-1239):
Find the following:
What percent of the young girls reported that they drink milk?
What percent of the young girls were in the 2007-2009 survey?
What percent of the young girls who reported that they drink milk were in the 2007-2009 survey?
Drinks Fluid Milk
Nationwide Food Survey Years
2005-2006 2007-2009 2010-2012
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Practice Problems Exam 1
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4. What percent of the young girls in 2007-2009 reported that they drink milk?
b. What is the marginal distribution of milk consumption?
12. It's the last inning of an important baseball game. The home team is losing by a run, the bases are loaded
and the manager needs a pinch hitter. Two batters are available to pinch hit. Here are their statistics:
vs Left-handed pitching vs Right-handed pitching
33 for 103
28 for 81
5 for 22
45 for 151
12 for 32
33 for 119
Based on their overall batting averages and their batting averages against right-handed and left-handed
pitchers, who would you select as the pinch hitter? What is this phenomenon called?
13. The mean SAT verbal score of next year's freshmen entering the local university is 600. It is also known
that 69.5% of these freshmen have scores that are less than 625. If the scores can be described by a normal
model, what is the standard deviation of the scores?
14. Two students are enrolled in an introductory statistics course at the University of Florida. The first student
is in a morning section and the second student is in an afternoon section. If the student in the morning
section takes a midterm and earns a score of 76, while the student in the afternoon section takes a midterm
with a score of 72, which student has performed better compared to the rest of the students in his respective
class? Assume that the test scores can be described by a normal model. For the morning class, the class
mean was 64 with a standard deviation of 8. For the afternoon class, the class mean was 60 with a standard
deviation of 7.5.
15. Suppose that a Normal model describes the acidity (pH) of rainwater, and the water tested after last week's
storm had a z-score of 1.8. This means that the acidity of that rain
a. had a pH of 1.8
b. varied with a standard deviation of 1.8
c. had a pH 1.8 higher than the average rainfall
d. had a pH 1.8 times that of average rainwater
e. had a pH 1.8 standard deviations higher than that of average rainwater
16. The highway gas mileage B, measured in miles per gallon (mpg), of 26 models of midsize cars, have the
following summary statistics: B œ 26.54 mpg, median œ 26 mpg, = œ 3.04 mpg, IQR œ 3 mpg. If you
convert gas mileage B from miles per gallon to B8/A which is measured in miles per liter, what are the new
values of the summary statistics? (3.785 liters œ 1 gallon).
17. A local plumber makes house calls. She charges $30 to come out to the house and $40 per hour for her
services. For example, a 4-hour service call costs $30 + $40(4) = $190.
a. The table shows summary statistics for the past month. Fill in the table to find out the cost of the service
Statistic Hours of Service Call Cost of Service Call
Stan Dev
b. This past month, the time the plumber spent on a particular service call had a z-score of  1.50. What
is the z-score for the cost of the service call?
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Practice Problems Exam 1
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18. In 2010 the Department of Education published the Digest for Education Statistics, a collection of
information about education in the United States. They reported the average amount (dollars per student)
spent by public schools in each state and Washington, D.C.during the school year 2007-2008. The data was
recorded according to whether the state lies east or west of the Mississippi River. A back-to-back stem and
leaf display of the data is shown below. 6|7 denotes $6,700.
a. Which states, Eastern or Western, tend to spend more?
b. Western states median = ? Eastern states Q" = ?
ST 311
Practice Problems Exam 1
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19. A medical researcher wanted to examine the relationship between the amount of sunshine (B) in hours, and
incidence of melanoma, a type of skin cancer (C). She found data showing the number of melanoma cases
detected per 100,000 of population and the average daily sunshine in eight counties around the country. The
data are shown below.
Average daily sunshine 5 7
6 7
4 3
Melanoma per 100,000 7 11 9 12 15 10 7 5
a. Which scatterplot below is the scatterplot of the above data?
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Practice Problems Exam 1
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Given that  ÐB3  BÑÐC3  CÑ œ $', what is the correlation < between Average daily sunshine and
Melanoma per 100,000?
20. Suppose that all major league baseball players had exactly 5 times as many runs batted in as home runs.
Describe what information this provides about the correlation between runs batted in and home runs.
21. Outdoor temperature influences natural gas consumption for the purpose of heating a house. The usual
measure of the need for heating is heating degree days. The number of heating degree days for a particular
day is the number of degrees the average temperature for that day is below 65°F, where the average
temperature for a day is the mean of the high and low temperatures for that day. An average temperature of
20°F, for example, corresponds to 45 heating degree days. A homeowner interested in switching to solar
heating panels collects the following data on her natural gas use for the months October through June, where
x is heating degree days per day for the month and y is gas consumption per day in hundreds of cubic feet.
Calculate the correlation coefficient r and interpret its value; draw a scatterplot of the data.
22. Each of the following statements contains a blunder. In each case explain what is wrong.
a. “There is a high correlation between the sex of American workers and their income."
b. “We found a high correlation (r œ 1.09) between students' ratings of faculty teaching and ratings made by
other faculty members."
c. “The correlation between planting rate and yield of corn was found to be r œ .23 bushel."
23. Suppose that a PE teacher collected data about the students in his class. Some of these variables included
number of pull-ups in 1 minute, number of push-ups in 1 minute, number of sit-ups in 1 minute, and weight.
The teacher then calculated the correlation between number of pull-ups and each of the other three variables
and found the following correlations: < œ !Þ*ß < œ  !Þ&ß < œ !Þ$ Which correlation goes with which
variable? Explain.
24. The following scatterplots based on data from a recent season show the association between the number of
points scored by the teams in the National Basketball Association (NBA) and three different explanatory
variables (number of field goals, free throw percentage, and number of free throws). The correlations are (in
no particular order) < œ !Þ#!ß < œ !Þ'"ß < œ !Þ)*. Match the correlations to the scatterplots.
ST 311
Practice Problems Exam 1
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Consider the following histograms of variables labeled X1, X2 and X3:
25. The median for variable X2 would be around
a. 10 b. 305 c. 250 d. impossible to tell
26. The third quartile for variable X1 would be around
a. 12 b. 8 c. 5 d. 15
27. The distribution in which the mean and median are most different would be
a. X1 b. X2 c. X3 d. It is impossible to tell.
28. The standard deviation for variable X1 would be
a. About the same as the standard deviation for variable X2.
b. Smaller than the standard deviation for variable X2.
c. Larger than the standard deviation for variable X2.
d. It is impossible to tell.
29. The histograms above are the results of questions asked of a group of undergraduate students. Match the
histogram (X1, X2, or X3) above to the appropriate question below.
a. How many hours did you work at a job last week?______
b. What is your shoe size? _______
c. How much did you spend on textbooks (in dollars) this semester? ______
ST 311
Practice Problems Exam 1
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30. Consider the following scatterplot.
Which of the following is a plausible value for the correlation coefficient between weight and MPG?
a. -0.9 b. -1.0 c. +0.2 d. +0.9 e. +0.7
1. b 2. 2.5% (6' 1"=73" is how many standard deviations above the mean?)
3. a) 2.8 b) median 2.94; quartiles: since there are 7 (odd) observations, include the overall median in each half
of the data) Q" is the median of the smallest 4 observations so Q" œ "Þ)&#Þ$(
œ #Þ""à Q$ is the median of the
largest 4 observations so Q$ œ $Þ"%$Þ'
- 2.11 = 1.26
4. .87 5. a
6. a) the median will probably be unaffected; the mean will be larger b) the range and standard deviation will
increase, the IQR will be unaffected
7.Skewed to the right.
8. a. The first step is to order the data. Then compute the overall median. Since there are 27 observations,
the median is the observation in position 14: median œ 85. Compute Q" : we want the median of the
lower half. Since we have an odd number of observations (27), include the overall median in both
halves of the data. There are 14 observations in the lower half, including the overall median. The
median of these lower 14 observations is the mean of the 2 middle observations in positions 7 and 8, so
Q" œ (!(#
œ (".
Note that U$ is the median of the 14 observations in the upper half, including the overall median. So
U$ is the mean of the 2 middle observations in positions 20 and 21: U$ œ ))*"
œ 89.5.
IQR = U$  U" œ 89.5 - 71 = 18.5; 1.5*IQR = 27.75.
Boundaries for outliers: U"  "Þ&‡MUV œ ("  #(Þ(& œ %$Þ#& à U$  "Þ&‡MUV œ )*Þ&  #(Þ(& œ
""(Þ#& .
Since the smallest observation is 46 and the largest observation is 98, there are no outliers. See boxplot
below (the diamonds above the box represent the individual data values).
ST 311
Practice Problems Exam 1
page 9
Test Scores
9. z = -1.27 ; x = 2.595 years. 10. a. .0668 b. z = -0.675 ; x = 3.16. 11. a1. 56.9% a2. 38.9% a3. 41.1% a4.
60% b. Yes: 56.9%; No: 43.1%. 12. Player A overall batting avg. = .320; Player B overall batting avg.=.298.
Choose player A. Player A vs right-handed pitchers = .227, Player B vs right-handed pitchers = .277; Player A
vs left-handed pitchers = .346; Player B vs left-handed pitchers = .375. Player B has the higher batting average
against both right-handed and left-handed pitchers; choose Player B. Simpson's paradox. 13. 0.51 = (625600)/5 Ê 5 œ 49.02 14.. z1 =(76-64)/8=1.5 ; z2 =(72-60)/7.5=1.6 . The student in the afternoon section
performed better.
15. e. 16. B8/A œ 7.01 miles per liter; median8/A œ 6.87 miles per liter; =8/A œ .803
miles per liter; MUV8/A œ Þ793 miles per liter.
17. a.
Statistic Hours of Service Call Cost of Service Call
Stan Dev
b.  1.50
18. a. Eastern b. West median œ $5ß 950, East Q" = $6,000
 ÐB3 BÑÐC3 CÑ
19. a. i) b. < œ
where =B and =C are, respectively, the standard deviation of the B-data and C=B ‡=C
Using a calculator to compute the standard deviations, we have =B œ "Þ''* and =C œ $Þ#!(. Therefore
< œ "( "Þ''*‡$Þ#!(
œ Þ*'"
20. Since V?8= ,+>>/. 38 œ &‡297/ <?8=, there is an exact linear relationship between V?8= ,+>>/. 38 and
297/ <?8=Þ Therefore, there is a perfect correlation, so the correlation is  " or  ". Since the coefficient “&”
is positive, the correlation is  ".
21. r œ .989. There is a strong positive linear relationship between heating degree days and gas
22. a. The correlation we are studying measures the linear relationship between 2 quantitative
variables; sex is a categorical variable.
b.  1 Ÿ r Ÿ 1 is violated.
c. r has no units.
23. < œ !Þ*: number of push-ups. Someone who is good at pull-ups should be good at push-ups since both
measure arm strength.
< œ  !Þ&: weight. You would expect a negative association between pull-ups and weight because it is
more difficult to do pull-ups when you are heavier.
< œ !Þ$: number of sit-ups. You would expect a positive association between pull-ups and sit-ups because
they both measure physical fitness, but the association would not be as strong as the association between
pull-ups and push-ups since they are different forms of exercise.
ST 311
Practice Problems Exam 1
25. b
26. a
27. c
28. b
29. a. X3 b. X1 c. X2
30. a
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