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```Chapter 9
Review Problems
Problem #1

Jack is taking Math 110 this semester and
wants to evaluate his progress using data
from quizzes he has taken so far. His quiz
scores are as follows: 75, 80, 60, 90, 100,
40, 75, 95, 60, 75.
Find the following:
a.) mean
b.) median
c.) mode
d.) range
e.) standard deviation
Problem #2

The normal monthly temperatures (in
degrees Fahrenheit) for the month of July is
listed for 20 different U.S. cities.
95.1
95.7
77.1
83.4
90.9
81.0
79.4
88.3
78.9
87.2
85.6
96.2
89.5
79.8
77.3
93.3
90.8
86.1
88.7
79.8
Find the mean, median, and mode of this
data.
Problem #3

Using the
employment
information in the
table at right for
Omega Corporation,
find the mean, mode,
and estimated
median of the
grouped data.
Years of
Service
Number of
Employees
1–5
15
6 – 10
32
11 – 15
47
16 – 20
29
21 – 25
18
26 – 30
6
Problem #4

The following
distribution of
commuting distances
was obtained for a
sample of Mutual of
Find the mean and
standard deviation for
the commuting
distances.
Distance
(miles)
Frequency
1.0 – 3.0
2
3.0 – 5.0
6
5.0 – 7.0
12
7.0 – 9.0
50
9.0 – 11.0
35
11.0 – 13.0
15
13.0 – 15.0
5
Problem #5

Find the percent of the total area under a
normal curve that is contained in the
interval between z = -1.95 and z = -.25.
Problem #6

Find the z-score such that 3.5% of the
total area is to the left of z.
Problem #7

Find a z-score such that 4% of the total
area is to the right of z.
Problem #8

Computers are shut down for certain
periods of time for routine maintenance,
installation of new hardware, and so on.
The down times for a particular computer
are normally distributed with a mean of
1.5 hours and a standard deviation of 0.4
hour. What percentage of the down times
exceed 2 hours?
Problem #9

According to the November 1993 issue of
Harper’s magazine, kids spend from 1200
to 1800 hours a year in front of the
television set. Suppose the time spent by
kids in front of the television set is
normally distributed with a mean equal to
1500 hours and a standard deviation equal
to 100 hours. What percentage spend
between 1400 and 1600 hours?
Problem #10

The length of useful life of a fluorescent
tube used for indoor gardening is normally
distributed. The useful life has a mean of
600 hours and a standard deviation of 40
hours. A company installs 10,000 of these
fluorescent tubes. Find the approximate
number of tubes that will:
a.) last more than 700 hours.
b.) last less than 600 hours.
(Solutions available in SSCC Library at the Reserve Desk.)
1.)
2.)
3.)
mean = 75
median = 75
mode = 75
range = 60
standard deviation = 18.105
mean = 86.205
median = 86.65
mode = 79.8
mean = 13.714
mode = occurs in interval 11-15 years
estimated mode = 13
median = occurs in interval 11-15 years
estimated median = 13
(Solutions available in SSCC Library at the Reserve Desk.)
4.)
mean = 8.8
standard deviation = 2.369
5.) .3757
6.) z = -1.81
7.) z = 1.75
8.) 10.56%
9.) 68.26%
10.) a.)
62 tubes
b.) 5000 tubes
```
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