9.
In the previous question, the mean finish time is 2.164 hours and the standard deviation is
0.85 hours.
The distribution is skewed right.
What are the mean, standard deviation, and
shape of the distribution of
z
-scores of the same data?
(a) Mean = 2.164, Standard deviation = 0.85, skewed right
(b)
Mean = 2.164, Standard deviation = 0.85, skewed left
(c) Mean = 2.164, Standard deviation = 0.85, approximately normal
(d) Mean = 0, Standard deviation = 1, skewed right
(e) Mean = 0, Standard deviation = 1, approximately normal
2.40
2.35
2.30
2.25
2.20
2.15
2.10
1.0
0.8
0.6
0.4
0.2
0.0
Finish time (hours)
Cumulative relative frequency

10.
Kitchen appliances don’t last forever.
The lifespan of all microwave oven
s sold in the United
States is approximately Normally distributed with a mean of 9 years and a standard deviation
of 2.5 years.
What percentage of the ovens last more than 10 years?

82
The Practice of Statistics, 4/e- Chapter 2
© 2011 BFW Publishers
Part 2:
Free Response
Show all your work.
Indicate clearly the methods you use, because you will be graded on the
correctness of your methods as well as on the accuracy and completeness of your results and
explanations.
Lamar is shopping for a used car, and he’s interes
ted in determining the typical mileage on cars
that are three or four years old.
He looks at an online car-buying site and compares the number
of miles on 30 cars that are three years old to 30 cars that are four years old.
His results are
summarized by Minitab below.
All values are in thousands of miles.
Descriptive Statistics: Mileage on Four year old cars and Three year old cars
Variable
N
Mean
StDev
Minimum
Q1
Median
Q3
Four year old cars
30
56.68
17.82
23.60
47.80
54.70
64.50
Three year old cars
30
33.33
12.70
14.10
22.33
32.10
39.23
Both distributions are approximately Normally distributed.
11.
One car that Lamar is interested in is four years old and has been driven 40 thousand miles.
Another one is three years old and has 30 thousand miles on it.
How does the number of
miles on these cars compare, relative to other cars of the same age?
Provide appropriate
statistical calculations to support your answer.
12
Based on the information above, estimate the number of four year old cars Lamar looked at
that had been driven more than 42 thousand miles.
13.
Estimate the 60
th
percentile for mileage on the cars Lamar found that were four years old.
Maximum
100.30
66.40

© 2011 BFW Publishers
The Practice of Statistics, 4/e- Chapter 2
83
14.
A researcher wishes to calculate the average height of patients suffering from a particular
disease.
From patient records, the mean was computed to be 156 cm, with a standard
deviation of 5 cm.
Further investigation reveals that the scale was misaligned, and that all
readings are 2 cm too large, for example, a patient whose height is really 180 cm was
measured as 182 cm.
Furthermore, the researcher would like to work with statistics based on
meters (1 meter = 100 centimeters).
What would be the revised values for the mean and
standard deviation of the patients’ heights?