Download Chapter 7 and Chapter 8 Practice

Chapter 7 and Chapter 8 Practice
1) The lengths of pregnancies are normally distributed with a mean of 264 days and a standard deviation of 15
days. If 36 women are randomly selected, find the probability that they have a mean pregnancy between 264
days and 266 days.
2) Assume that the heights of women are normally distributed with a mean of 63.6 inches and a standard
deviation of 2.5 inches. If 100 women are randomly selected, find the probability that they have a mean height
greater than 63.0 inches.
3) Assume that the heights of men are normally distributed with a mean of 69.5 inches and a standard deviation of
2.1 inches. If 36 men are randomly selected, find the probability that they have a mean height greater than 70.5
inches.
4) The body temperatures of adults are normally distributed with a mean of 98.6° F and a standard deviation of
0.60° F. If 25 adults are randomly selected, find the probability that their mean body temperature is less than 99°
F.
5) Assume that the salaries of elementary school teachers in the United States are normally distributed with a
mean of $32,000 and a standard deviation of $3000. If 100 teachers are randomly selected, find the probability
that their mean salary is less than $32,500.
6) Assume that blood pressure readings are normally distributed with a mean of 115 and a standard deviation of
8. If 100 people are randomly selected, find the probability that their mean blood pressure will be less than 117.
7) The average number of pounds of red meat a person consumes each year is 196 with a standard deviation of 22
pounds (Source: American Dietetic Association). If a sample of 50 individuals is randomly selected, find the
probability that the mean of the sample will be less than 200 pounds.
8) A coffee machine dispenses normally distributed amounts of coffee with a mean of 12 ounces and a standard
deviation of 0.2 ounce. If a sample of 9 cups is selected, find the probability that the mean of the sample will be
less than 12.1 ounces. Find the probability if the sample is just 1 cup.
Use the Central Limit Theorem to find the mean and standard error of the mean of the indicated sampling distribution.
9) The amounts of time employees of a telecommunications company have worked for the company are normally
distributed with a mean of 5.4 years and a standard deviation of 2.1 years. Random samples of size 12 are
drawn from the population and the mean of each sample is determined.
10) The monthly rents for studio apartments in a certain city have a mean of $920 and a standard deviation of $190.
Random samples of size 30 are drawn from the population and the mean of each sample is determined.
Provide an appropriate response.
11) The weights of people in a certain population are normally distributed with a mean of 157 lb and a standard
deviation of 23 lb. Find the mean and standard error of the mean for this sampling distribution when using
random samples of size 8.
12) The mean annual income for adult women in one city is $28,520 and the standard deviation of the incomes is
$5600. The distribution of incomes is skewed to the right. Find the mean and standard error of the mean for this
sampling distribution when using random samples of size 66. Round your answers to the nearest dollar.
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13) Find the critical value z c that corresponds to a 94% confidence level.
14) Determine the sampling error if the grade point averages for 10 randomly selected students from a class of 125
students has a mean of x = 2.8. Assume the grade point average of the 125 students has a mean of
µ = 3.5.
15) Find the margin of error for the given values of c, , and n.
c = 0.90, = 11.5, n = 120
16) A random sample of 150 students has a grade point average with a mean of 2.86. Assume the population
standard deviation is 0.78. Construct the confidence interval for the population mean, µ, if c = 0.98.
17) A random sample of 56 fluorescent light bulbs has a mean life of 645 hours. Assume the population standard
deviation is 31 hours. Construct a 95% confidence interval for the population mean.
18) A group of 40 bowlers showed that their average score was 192. Assume the population standard deviation is 8.
Find the 95% confidence interval of the mean score of all bowlers.
19) In a random sample of 60 computers, the mean repair cost was $150. Assume the population standard deviation
is $36.
a) Construct the 99% confidence interval for the population mean repair cost.
b) If the level of confidence was lowered to 95%, what will be the effect on the confidence interval?
20) In a sample of 10 randomly selected women, it was found that their mean height was 63.4 inches. From
previous studies, it is assumed that the standard deviation is 2.4 and that the population of height
measurements is normally distributed. Construct the 95% confidence interval for the population mean.
21) The numbers of advertisements seen or heard in one week for 30 randomly selected people in the United States
are listed below. Construct a 95% confidence interval for the true mean number of advertisements. Assume that
is 159.5.
598
494
441
595
728
690
684
486
735
808
481
298
135
846
764
317
649
732
582
677
734
588
590
540
673
727
545
486
702
703
22) The standard IQ test has a mean of 96 and a standard deviation of 14. We want to be 99% certain that we are
within 4 IQ points of the true mean. Determine the required sample size.
23) A nurse at a local hospital is interested in estimating the birth weight of infants. How large a sample must she
select if she desires to be 95% confident that the true mean is within 3 ounces of the sample mean? The standard
deviation of the birth weights is known to be 6 ounces.
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24) In order to set rates, an insurance company is trying to estimate the number of sick days that full time workers
at an auto repair shop take per year. A previous study indicated that the standard deviation was 2.8 days. How
large a sample must be selected if the company wants to be 95% confident that the true mean differs from the
sample mean by no more than 1 day?
25) Find the critical value, tc for c = 0.99 and n = 10.
26) Find the critical value, tc, for c = 0.95 and n = 16.
27) Find the critical value, tc, for c = 0.90 and n = 15.
28) Find the value of E, the margin of error, for c = 0.99, n = 16 and s = 2.6.
29) Find the value of E, the margin of error, for c = 0.95, n = 15 and s = 5.6.
30) Construct the indicated confidence interval for the population mean µ using the t-distribution.
c = 0.99, x = 22.4, s = 3.8, n = 19
31) In a random sample of 28 families, the average weekly food expense was $95.60 with a standard deviation of
$22.50. Determine whether a normal distribution or a t-distribution should be used or whether neither of these
can be used to construct a confidence interval. Assume the distribution of weekly food expenses is normally
shaped.
32) A random sample of 40 college students has a mean earnings of $3120 with a standard deviation of $677 over
the summer months. Determine whether a normal distribution or a t-distribution should be used or whether
neither of these can be used to construct a confidence interval.
33) Construct a 90% confidence interval for the population mean, µ. Assume the population has a normal
distribution. A sample of 15 randomly selected students has a grade point average of 2.86 with a standard
deviation of 0.78.
34) Construct a 98% confidence interval for the population mean, µ. Assume the population has a normal
distribution. A random sample of 20 college students has mean annual earnings of $3140 with a standard
deviation of $686.
35) Construct a 99% confidence interval for the population mean, µ. Assume the population has a normal
distribution. A group of 19 randomly selected students has a mean age of 22.4 years with a standard deviation
of 3.8 years.
36) A random sample of 10 parking meters in a beach community showed the following incomes for a day. Assume
the incomes are normally distributed.
$3.60 $4.50 $2.80 $6.30 $2.60 $5.20 $6.75 $4.25 $8.00 $3.00
Find the 95% confidence interval for the true mean.
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37) A coffee machine is supposed to dispense 12 ounces of coffee in each cup. An inspector selects a random
sample of 40 cups of coffee and finds they have an average amount of 12.2 ounces with a standard deviation of
0.3 ounce. Use a 99% confidence interval to test whether the machine is dispensing acceptable amounts of
coffee.
38) The numbers of advertisements seen or heard in one week for 30 randomly selected people in the United States
are listed below. Construct a 95% confidence interval for the true mean number of advertisements.
598
494
441
595
728
690
684
486
735
808
481
298
135
846
764
317
649
732
582
677
734
588
590
540
673
727
545
486
702
703
39) When 410 college students were surveyed,150 said they own their car. Find a point estimate for p, the
population proportion of students who own their cars.
40) A survey of 700 non-fatal accidents showed that 231 involved the use of a cell phone. Find a point estimate for
p, the population proportion of non-fatal accidents that involved the use of a cell phone.
41) A survey of 2210 golfers showed that 389 of them are left-handed. Find a point estimate for p, the population
proportion of golfers that are left-handed.
42) In a survey of 2480 golfers, 15% said they were left-handed. The survey's margin of error was 3%. Construct a
confidence interval for the proportion of left-handed golfers.
43) The Federal Bureau of Labor Statistics surveyed 50,000 people and found the unemployment rate to be 5.8%.
The margin of error was 0.2%. Construct a confidence interval for the unemployment rate.
44) When 490 college students were surveyed, 130 said they own their car. Construct a 95% confidence interval for
the proportion of college students who say they own their cars.
45) A survey of 300 fatal accidents showed that 123 were alcohol related. Construct a 98% confidence interval for
the proportion of fatal accidents that were alcohol related.
46) A survey of 400 non-fatal accidents showed that 181 involved the use of a cell phone. Construct a 99%
confidence interval for the proportion of fatal accidents that involved the use of a cell phone.
47) A survey of 280 homeless persons showed that 63 were veterans. Construct a 90% confidence interval for the
proportion of homeless persons who are veterans.
48) A survey of 2450 golfers showed that 281 of them are left-handed. Construct a 98% confidence interval for the
proportion of golfers that are left-handed.
49) A researcher at a major hospital wishes to estimate the proportion of the adult population of the United States
that has high blood pressure. How large a sample is needed in order to be 90% confident that the sample
proportion will not differ from the true proportion by more than 5%?
50) A manufacturer of golf equipment wishes to estimate the number of left-handed golfers. How large a sample is
needed in order to be 95% confident that the sample proportion will not differ from the true proportion by more
than 4%? A previous study indicates that the proportion of left-handed golfers is 9%.
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Answer Key
Testname: UNTITLED1
1)
2)
3)
4)
5)
6)
7)
8)
9)
10)
11)
12)
13)
14)
15)
16)
17)
18)
19)
0.2881
0.9918
0.0021
0.9996
0.9525
0.9938
0.9015
0.9332; 0.6915
5.4 years, 0.61 years
$920, $34.69
157, 8.13
$28,520, $689
±1.88
0.7
1.73
(2.71, 3.01)
(636.9, 653.1)
(189.5, 194.5)
a) ($138, $162)
b) A decrease in the level of confidence will decrease the width of the confidence interval.
20)
21)
22)
23)
24)
25)
26)
27)
28)
29)
30)
31)
32)
33)
34)
35)
36)
37)
(61.9, 64.9)
(543.8, 658.0)
82
16
31
3.250
2.131
1.761
1.92
3.10
(19.9, 24.9)
Use the t-distribution.
Use normal distribution.
(2.51, 3.21)
($2751, $3529)
(19.9, 24.9)
($3.39, $6.01)
(12.1, 12.3) Because the interval does not contain the desired amount of 12 ounces, the machine is not working
properly.
(543.8, 658.0)
0.366
0.330
0.176
(0.12, 0.18)
(0.058, 0.060)
(0.226, 0.304)
(0.344, 0.476)
(0.388, 0.517)
(0.184, 0.266)
38)
39)
40)
41)
42)
43)
44)
45)
46)
47)
5
Answer Key
Testname: UNTITLED1
48) (0.100, 0.130)
49) 271
50) 197
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