# Name Date ______ 1. A medical researcher is working

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```					Name: __________________________ Date: _____________

1. A medical researcher is working on a new treatment for a certain type of cancer. The
average survival time after diagnosis on the standard treatment is two years. In an early
trial, she tries the new treatment on three subjects who have an average survival time
after diagnosis of four years. Although the survival time has doubled, the results are
not statistically significant, even at the 0.10 significance level. Suppose, in fact, that
the new treatment does increase the mean survival time in the population of all patients
with this particular type of cancer. Which of the following statements is true?
A) A type I error has been committed.
B) A type II error has been committed.
C) No error has been committed.

2. A sprinkler system is being installed in a large office complex. Based on a series of test
runs, a 99% confidence interval for , the average activation time of the sprinkler
system (in seconds), is found to be (22, 28). Determine whether each of the following
statements is true or false.
A) The 99% confidence level implies that P(22 <  < 28) = 0.99.
B) The 99% confidence level implies that P(22 < x < 28) = 0.99.
C) The 99% confidence level implies that 99% of the sample means ( x ) obtained from
repeated sampling would fall between 22 and 28.
D) If a 95% confidence interval were calculated from the same data, (23, 27) would be a
possible interval.

3. A simple random sample of 100 athletes is selected from a large high school. In the
sample, there are 15 football players. What is the standard error of the sample
proportion of football players?
A) 0.00128
B) 0.0357
C) 0.05
D) 0.357

4. Determine whether each of the following statements is true or false.
A) The margin of error for a 95% confidence interval for the mean  increases as the
sample size increases.
B) The margin of error for a confidence interval for the mean , based on a specified
sample size n, increases as the confidence level decreases.
C) The margin of error for a 95% confidence interval for the mean  decreases as the
population standard deviation decreases.
D) The sample size required to obtain a confidence interval of specified margin of error
m, increases as the confidence level increases.

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5. The test statistic for a two-sided significance test for a population mean is z = –2.12.
What is the corresponding P-value?
A) 0.017
B) 0.034
C) 0.483
D) 0.983

6. A simple random sample of 85 students is taken from a large university on the West
Coast to estimate the proportion of students whose parents bought a car for them when
they left for college. When interviewed, 51 students in the sample responded that their
parents bought them a car. What is a 95% confidence interval for p, the population
proportion of students whose parents bought a car for them when they left for college?
A) (0.296, 0.504)
B) (0.463, 0.737)
C) (0.496, 0.704)
D) (0.513, 0.687)

Use the following to answer questions 7-9:

The distribution of the amount of money undergraduate students spend on books for a term is
slightly right skewed, with a mean of \$400 and a standard deviation of \$80.

7. If a student is selected at random, what is the probability that this student spends more
than \$425 on books?
A) 0.1125
B) 0.3773
C) 0.6227
D) This cannot be determined from the information given.

8. If a simple random sample of 100 undergraduate students is selected, what is the
probability that these students spend more than \$425 on books, on average?
A) 0.00089
B) 0.2353
C) 0.3773
D) This cannot be determined from the information given.

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9. In a simple random sample of 100 undergraduate students, what is the expected value of
the sample mean amount of money spent on books?
A) \$400
B) Anywhere between \$320 and \$480.
C) Anywhere between \$392 and \$408.
D) This cannot be determined from the information given.

Use the following to answer questions 10-12:

During the last student elections at a certain college, 45% of the students voted for the
democratic student party. A simple random sample of students from this college is to be selected.

10. If 12 students are to be selected, what is the distribution of the number of students in the
sample who voted for the democratic student party?

11. If 12 students are to be selected, what is the probability that more than 7 students in the
sample voted for the democratic student party?

12. If 120 students are to be selected, what is the (approximate) distribution of the number
of students in the sample who voted for the democratic student party?

Use the following to answer questions 13-14:

A simple random sample of 25 male faculty members at a large university reveals that 10 of
them feel that the university is supportive of female and minority faculty. An independent
simple random sample of 20 female faculty members reveals that only 5 of them feel that the
university is supportive of female and minority faculty. Let p1 and p2 represent the proportions
of all male and female faculty members at the university who feel that the university is
supportive of female and minority faculty at the time of the survey.

13. Is there evidence that the proportion of male faculty members who feel the university is
supportive of female and minority faculty is larger than the corresponding proportion of
female faculty members? To determine this, test the hypotheses H0: p1 = p2 versus Ha:
p1 > p2. What can we say about the P-value of the hypothesis test?
A) The P-value is smaller than 0.001.
B) The P-value is between 0.001 and 0.01.
C) The P-value is between 0.01 and 0.05.
D) The P-value is larger than 0.05.

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14. What is the margin of error for a 95% plus four confidence interval for p1 – p2?
A) m = 0.134
B) m = 0.220
C) m = 0.263
D) m = 0.345

15. An engineer has designed an improved light bulb. The previous design had an average
lifetime of 1200 hours. Based on a sample of 2000 of these new bulbs, the average
lifetime was found to be 1201 hours. Although the difference is quite small, the effect
was statistically significant. What is the best explanation?
A) New designs typically have more variability than standard designs.
B) The sample size is very large, so that even a small difference can be detected.
C) The mean of 1200 is large.
D) The relative improvement in average lifetime is 0.000083, which is much smaller
than 0.05.

Use the following to answer questions 16-17:

Assume that sample data, based on two independent samples of size 25, gives us x1 = 505, x2
= 515, s1 = 23, and s2 = 28.

16. What is a 95% confidence interval (use the conservative value for the degrees of
freedom) for 2 – 1?
A) (–2.40, 22.40)
B) (–4.96, 24.96)
C) (–4.57, 24.57)
D) (5.79, 14.21)

17. Determine whether each of the following statements is true or false.
A) Based on the confidence interval, we can conclude, at the 5% significance level, that
there is no difference between the two population means, 2 and 1.
B) The margin of error for the difference between the two sample means would be
smaller if we were to take larger samples.
C) If we were to use the unpooled t test with the more accurate approximation for the
degrees of freedom (used in software), the degrees of freedom would be 51.
D) If a 99% confidence interval were calculated instead of the 95% interval, it would
include more values for the difference between the two population means.

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18. The square footage of the several thousand apartments in a new development is
advertised to be 1250 square feet, on average. A tenant group thinks that the
apartments are smaller than advertised. They hire an engineer to measure a sample of
apartments to test their suspicions. Let  represent the true average area (in square
feet) of these apartments. What are the appropriate null and alternative hypotheses?
A) H0:  = 1250 vs. Ha:  < 1250
B) H0:  = 1250 vs. Ha:   1250
C) H0:  = 1250 vs. Ha:  > 1250

19. A simple random sample of 60 blood donors is taken to estimate the proportion of
donors with type A blood with a 95% confidence interval. In the sample, there are 10
people with type A blood. What is the margin of error for this confidence interval?
A) 0.048
B) 0.079
C) 0.094
D) 1.96

20. The test statistic for a significance test for a population mean is z = –2.12. The
hypotheses are H0:  = 10 versus Ha:  > 10. What is the corresponding P-value?
A) 0.017
B) 0.034
C) 0.483
D) 0.983

Use the following to answer questions 21-23:

Chromosome defect A occurs in only one out of 200 adult males. A random sample of 100 adult
males is selected. Let the random variable X represent the number of males in the sample who
have this chromosome defect.

21. What is the exact distribution of the random variable X?

22. Can we use the normal approximation to answer probability questions about the random
variable X? Briefly explain why or why not.

23. What are the mean and standard deviation of the random variable X?

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Use the following to answer questions 24-25:

In the university library elevator there is a sign indicating a 16-person limit as well as a weight
limit of 2500 lbs. Suppose that weight of students, faculty, and staff is approximately normally
distributed with a mean weight of 150 lbs. and a standard deviation of 27 lbs.

24. What is the probability that the random sample of 16 people in the elevator will exceed
the weight limit?

25. When the elevator is full, we can think of the 16 people in the elevator as a simple
random sample of people on campus. What average weight for these 16 people in the
elevator will result in the total weight exceeding the weight limit of 2500 lbs.?

26. The tail area above a test statistic value of z = 1.812 is 0.035. Determine whether each of
the following statements is true or false.
A) If the alternative hypothesis is of the form Ha:  > 0, the data are statistically
significant at significance level  = 0.05.
B) If the alternative hypothesis is of the form Ha:  > 0, the data are statistically
significant at significance level  = 0.10.
C) If the alternative hypothesis is of the form Ha:   0, the data are statistically
significant at significance level  = 0.05.
D) If the alternative hypothesis is of the form Ha:   0, the data are statistically
significant at significance level  = 0.10.

27. Ten years ago, at a small high school in Alabama, the mean Math SAT score of all high
school students who took the exam was 490 with a standard deviation of 80. This year,
the Math SAT scores of a random sample of 25 students who took the exam are
obtained. The mean score of these 25 students is x = 525. To determine if there is
evidence that the scores in the district have improved, the hypotheses H0:  = 490 versus
Ha:  > 490 are tested at the 5% significance level. The P-value is found to be 0.014.
Suppose that the average Math SAT score of all high school students at this high school
is in fact equal to 505. Which of the following statements is true?
A) A type I error has been committed.
B) A type II error has been committed.
C) No error has been committed.

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28. In a test of statistical hypotheses, what does the P-value tell us?
A) If the null hypothesis is true.
B) If the alternative hypothesis is true.
C) The largest level of significance at which the null hypothesis can be rejected.
D) The smallest level of significance at which the null hypothesis can be rejected.

Use the following to answer questions 29-31:

A researcher wished to compare the average amount of time spent in extracurricular activities by
high school students in a suburban school district with that in a school district of a large city.
The researcher obtained a simple random sample of 60 high school students in a large suburban
school district and found the mean time spent in extracurricular activities per week to be 6 hours
with a standard deviation of 3 hours. The researcher also obtained an independent simple
random sample of 40 high school students in a large city school district and found the mean time
spent in extracurricular activities per week to be 4 hours with a standard deviation of 2 hours.
Let 1 and 2 represent the mean amount of time spent in extracurricular activities per week by
the populations of all high school students in the suburban and city school districts, respectively.
Assume two sample t procedures are safe to use.

29. What is a 95% confidence interval for 1 – 2? (Use the conservative value for the
degrees of freedom.)
A) 2 ± 0.5 hours
B) 2 ± 0.84 hours
C) 2 ± 1.01 hours
D) 2 ± 1.34 hours

30. Suppose the researcher had wished to test the hypotheses H0: 1 = 2 versus Ha: 1  2.
What can we say about the value of the P-value?
A) P-value < 0.01
B) 0.01 < P-value < 0.05
C) 0.05 < P-value < 0.10
D) P-value > 0.10

31. If we had used the more accurate software approximation to the degrees of freedom,
what would be the number of degrees of freedom for the two sample t procedures?
A) 39
B) 59
C) 97.998
D) 99.286

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32. Is the mean height for all adult American males between the ages of 18 and 21 now over
6 feet? Let  represent the population mean height of all adult American males
between the ages of 18 and 21. What are the appropriate null and alternative hypotheses
A) H0:  = 6 vs. Ha:  < 6
B) H0:  = 6 vs. Ha:   6
C) H0:  = 6 vs. Ha:  > 6

Use the following to answer questions 33-34:

Do students tend to improve their SAT Mathematics (SAT-M) score the second time they take
the test? A random sample of four students who took the test twice received the following
scores.

Student                   1         2           3        4
First score               450       520         720      600
Second score              440       600         720      630

Assume that the change in SAT-M score (second score – first score) for the population of all
students taking the test twice is normally distributed.

33. Suppose we do not believe that students tend to improve their SAT-M score the second
time they take the test. Based on the confidence interval previously calculated, we wish
to test H0:  = 0 versus Ha:   0 at the 5% significance level. Determine which of the
following statements is true:
A) We cannot make a decision since the confidence interval is so wide.
B) We cannot make a decision since the confidence level we used to calculate the
confidence interval is 90%, and we would need a 95% confidence interval.
C) We accept H0, since the value 0 falls in the 90% confidence interval and would
therefore also fall in the 95% confidence interval.
D) We reject H0, since the value 0 falls in the 90% confidence interval.

34. What is a 90% confidence interval for , the mean change in SAT-M score?
A) (–8.24, 58.24)
B) (–18.08, 68.08)
C) (–22.56, 72.56)
D) (–39.31, 89.31)

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Use the following to answer questions 35-37:

A simple random sample of 60 households in the city of Greenville (call this city 1) is taken. In
the sample, there are 45 households that decorate their houses with lights for the holidays. A
simple random sample of 50 households is also taken from the neighboring town of Brownsboro
(call this city 2). In the sample, there are 40 households that decorate their houses. We wish to
estimate the difference in proportions of households that decorate their houses with lights for the
holidays with a 95% confidence interval.

35. Under the null hypothesis of equality of the proportions of households that decorate
their houses in the two neighboring towns, what is the standard error of the difference in
sample proportions?
A) 0.040
B) 0.0795
C) 0.0802
D) 0.1125

36. What is a 95% confidence interval for the difference in population proportions of
households that decorate their houses with lights for the holidays?
A) (–0.181, 0.081)
B) (–0.206, 0.106)
C) (–0.231, 0.138)
D) (–0.255, 0.155)

37. What is the standard error of the difference in sample proportions?
A) 0.040
B) 0.0795
C) 0.0802
D) 0.1125

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38. A small New England college has a total of 400 students. The Math SAT is required
for admission, and the mean score of all 400 students is 620. The population standard
deviation is found to be 60. The formula for a 95% confidence interval yields the
interval 640 ± 5.88. Determine whether each of the following statements is true or
false.
A) If we repeated this procedure many, many times, only 5% of the 95% confidence
intervals would fail to include the mean Math SAT score of the population of all
students at this college.
B) The probability that the population mean will fall between 634.12 and 645.88 is 0.95.
C) The interval is incorrect. It is much too narrow.
D) If we repeated this procedure many, many times, x would fall between 634.12 and
645.88 about 95% of the time.

Use the following to answer question 39:

Central Middle School has calculated a 95% confidence interval for the mean height () of
11-year old boys at their school and found it to be 56 ± 2 inches.

39. Determine whether each of the following statements is true or false.
A) There is a 95% probability that  is between 54 and 58.
B) There is a 95% probability that the true mean is 56, and there is a 95% chance that
the true margin of error is 2.
C) If we took many additional random samples of the same size and from each
computed a 95% confidence interval for , approximately 95% of these intervals would
contain .
D) If we took many additional random samples of the same size and from each
computed a 95% confidence interval for , approximately 95% of the time  would fall
between 54 and 58.

40. An engineer has designed an improved light bulb. The previous design had an average
lifetime of 1200 hours. Using a sample of 2000 of these new bulbs, the average
lifetime of this improved light bulb is found to be 1201 hours. Although the difference
is quite small, the effect was statistically significant at the 0.05 level. Suppose that, in
fact, there is no difference between the mean lifetimes of the previous design and the
new design. Which of the following statements is true?
A) A type I error has been committed.
B) A type II error has been committed.
C) No error has been committed.

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Use the following to answer questions 41-44:

Your company is producing special battery packs for the most popular toy during the holiday
season. The life span of the battery pack is known to be normally distributed with a mean of 250
hours and a standard deviation of 20 hours.

41. What would typically be a better distribution than the normal distribution to model the
lifespan of these battery packs?

42. If a simple random sample of four battery packs is selected from your company and we
assume that their lifespans are independent, what is the probability that they all last
longer than 260 hours?

43. If a simple random sample of four battery packs is selected from your company, what is
the probability that the average lifetime of these four packs is longer than 260 hours?

44. What percentage of battery packs lasts longer than 260 hours?

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1.   B
2.   A) False, B) False, C) False, D) True
3.   B
4.   A) False, B) False, C) True, D) True
5.   B
6.   C
7.   D
8.   A
9.   A
10.   B(12, 0.45)
11.   0.1117
12.   N(54, 5.45)
13.   D
14.   C
15.   B
16.   C
17.   A) True, B) True, C) False, D) True
18.   A
19.   C
20.   D
21.   B(100, 0.005)
22.   No, np = (1/200)(100) = 0.5. The normal approximation can be used when np  10 and
n(1 – p)  10.
23.    X  np  (100)(0.005)  0.5 ,  X  np(1  p)  100(0.005)(0.995)  0.705
24.   0.1772
25.   156.25 lbs.
26.   A) True, B) True, C) False, D) True
27.   C
28.   D
29.   C
30.   A
31.   C
32.   C
33.   C
34.   C
35.   C
36.   B
37.   B
38.   A) False, B) False, C) False, D) False
39.   A) False, B) False, C) True, D) False
40.   A
41.   The Weibull distribution.
42.   0.00906
43.   0.1587

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44. 30.85%

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