# Stats Exercise Questions

11. An example of a measurement made in a nominal scale is:

a.the name of the college a student attends.

b.a student�s weight in kilograms.

c.a student�s class rank, such as 25th out of 364.

d.a student�s sex (male or female).

e.both (a) and (d).

12. The net asset value of a mutual fund has increased from $27 on December 31 to $33 now. The percent increase in value is:

a.about 22%.

b.about 18%.

c.about 1.2%.

d.about 122%.

e.about 82%.

13. The Center for Disease Control (CDC) sends four identical samples of bubonic plague cultures to the Acme Biological Analysis Laboratory, and asks the lab to measure the level of antigen in each sample. The lab is not told that the samples are identical. The lab reports antigen levels of 41, 123, 874, and 923. The CDC can conclude that measurements of antigen levels from this lab are:

a.biased.

b.confounded.

c.invalid.

d.unreliable.

14. Suppose all students who attend Stat 001 lectures during Fall Term 1997 are given packages of Little Chocolate Donuts at the beginning of each lecture, which they are encouraged to eat during the first five minutes of class. Students who attend Stat 001 lectures during Spring Term1998 will not be given donuts. Unfortunately, any systematic difference between Fall Term students and Spring Term students on the exams might be due to the fact that the spring term teacher is more skillful than the fall term teacher, rather than the donuts. This is an example of:

a.confounding.

b.the placebo effect.

c.stratification.

d.response error.

15. An important reason for the use of randomization in designing experiments is that it tends to:

a. reduce confounding.

b.allow double-blinding.

c.eliminate response error.

d.reduce the placebo effect.

16. A recent medical study found that people who drink more than 4 cups of coffee a day have more heart attacks thank people who drink less coffee or no coffee. This led some doctors to suspect that coffee may be a contributing factor in causing heart attacks. However, more careful analysis of the data showed that heavy coffee drinkers tend to smoke more than other people. This is an example of:

a.the placebo effect.

b.response error.

c.the double-blind technique.

d.a completely randomized design.

e.confounding.

17. It is hard to measure "intelligence." Let�s do it the easy way: measure height in inches, and call the result "intelligence." Not only is this method easy, it gives the same number every time we repeat the measurement on the same person. Measuring intelligence this way is:

a.not reliable and not valid.

b.highly reliable but not valid.

c.valid, but not reliable.

d.both valid and highly reliable.

18. An important ethical standard for any statistical study that uses human subjects is confidentiality. Confidentiality means that:

a.the names of the subjects are not known even to the people who carry our the study.

b.no results from the study are ever made public.

c.we are at least 95% confident in the study�s findings.

d.no results about individual subjects are made public, just overall results such as averages and percents for all subjects.

19. Any statistical study that uses human subjects requires informed consent. This means that:

a.a review board must agree that the study is worthwhile and will not harm the subjects.

b.the authors of the study must agree to inform the public of the study results.

c.the authors of the study must inform a review board about it and obtain the board�s consent to go ahead.

d.the nature of the study must be explained in advance to the subjects and they must voluntarily agree to take part.

20. Two essential features of all statistically designed experiments are:

a.compare several treatments; use the double-blind method.

b.compare several treatments; use chance to assign subjects to treatments.

c.always have a placebo group; use the double-blind method.

d.use a block design; use chance to assign subjects to treatments.

21. If we choose a simple random sample (SRS) from a population, we can be sure that the __________ which we compute from our SRS is a/an ____________ estimate of the population�s true ____________. We also know that we can get as high a degree of ___________ as desired by taking a large enough sample. The appropriate sequence of words to complete this statement is::

a.parameter, precise, statistic, unbiasedness

b.parameter, unbiased, statistic, precision

c.statistic, precise, parameter, unbiasedness

d.statistic, unbiased, parameter, precision

22. In an attempt to eliminate unintentional bias, some experiments use the "double-blind" method. This means that:

a.the subject does not know what treatment he received, but the experiment does.

b.the subject knows what treatment he received, but the experimenter does not.

c.neither the subject nor the experimenter know what treatment the subject received.

d.both the subject and the experimenter know what treatment the subject received.

23. The most important advantage of experiments over observational studies is:

a.confounding cannot occur in an experiment.

b.experiments can only be done in a laboratory.

c.experiments have both explanatory and response variables.

d.well-designed experiments give good evidence for causation.

24. An individual observation that lies far from the overall pattern of the other observations in a stemplot or histogram is called:

a.an outlier.

b.an extreme point.

c.a leaf.

d.confounded.

25. Increasing the sample size of an opinion poll will:

a.reduce the bias of the poll result.

b.increase the precision of the poll result.

c.reduce the effect of nonresponse on the poll.

d.all of the above.

e.a and b, but not c.

26. A sample of student opinion at a Big Ten university selects an SRS of 200 of the 30,000 undergraduate students and a separate SRS of 100 of the 5,000 graduate students. This kind of sample is called a:

a.simple random sample.

b.stratified random sample.

c.systematic random sample.

d.multistage sample.

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#### Solution Preview

11. An example of a measurement made in a nominal scale is:

a.the name of the college a student attends.

d.a student?s sex (male or female).

e.both (a) and (d).

12. The net asset value of a mutual fund has increased from $27 on December 31 to $33 now. The percent increase in value is:

a.about 22%.

13. The Center for Disease Control (CDC) sends four identical samples of bubonic plague cultures to the Acme Biological Analysis Laboratory, and asks the lab to measure the level of antigen in each sample. The lab is not told that the samples are identical. The lab reports antigen levels of 41, 123, 874, and 923. The CDC can conclude that measurements of antigen levels from this lab are:

d.unreliable.

14. Suppose all students who attend Stat 001 lectures during Fall Term 1997 are given packages of Little Chocolate Donuts at the beginning of each lecture, which they are encouraged to eat during the first five minutes of class. Students who attend Stat 001 lectures during Spring Term1998 will not be given donuts. ...

#### Solution Summary

The net asset value of a mutual fund has increased from $27 on December 31 to $33 now. The percent increase in value is...

Statistics: Various Probability Questions

Chapter 5

8. A sample of 2,000 licensed drivers revealed the following number of speeding violations.

Number of Violations Number of Drivers

0 1910

1 46

2 18

3 12

4 9

5 or more 5

Total 2000

a. What is the experiment?

b. List one possible event.

c. What is the probability that a particular driver had exactly two speeding violations?

d. What concept of probability does this illustrate?

66. A survey of undergraduate students in the School of Business at Northern University revealed

the following regarding the gender and majors of the students:

a. What is the probability of selecting a female student?

b. What is the probability of selecting a finance or accounting major?

c. What is the probability of selecting a female or an accounting major? Which rule of addition

did you apply?

d. Are gender and major independent? Why?

e. What is the probability of selecting an accounting major, given that the person selected

is a male?

f. Suppose two students are selected randomly to attend a lunch with the president of the

university. What is the probability that both of those selected are accounting majors?

Chapter 7

38. The accounting department at Weston Materials, Inc., a national manufacturer of unattached

garages, reports that it takes two construction workers a mean of 32 hours and a

standard deviation of 2 hours to erect the Red Barn model. Assume the assembly times follow

the normal distribution.

a. Determine the z values for 29 and 34 hours. What percent of the garages take between

32 hours and 34 hours to erect?

b. What percent of the garages take between 29 hours and 34 hours to erect?

c. What percent of the garages take 28.7 hours or less to erect?

d. Of the garages, 5 percent take how many hours or more to erect?

44. The number of passengers on the Carnival Sensation during one-week cruises in the

Caribbean follows the normal distribution. The mean number of passengers per cruise is

1,820 and the standard deviation is 120.

a. What percent of the cruises will have between 1,820 and 1,970 passengers?

b. What percent of the cruises will have 1,970 passengers or more

c. What percent of the cruises will have 1,600 or fewer passengers?

d. How many passengers are on the cruises with the fewest 25 percent of passengers?

60. In establishing warranties on HDTV sets, the manufacturer wants to set the limits so that

few will need repair at manufacturer expense. On the other hand, the warranty period must

be long enough to make the purchase attractive to the buyer. For a new HDTV the mean

number of months until repairs are needed is 36.84 with a standard deviation of 3.34

months. Where should the warranty limits be set so that only 10 percent of the HDTVs need

repairs at the manufacturer's expense?

The manufacturer of salad dressings uses machines to dispense the dressing into bottles that move along an assembly line. The machine is working well when 8 ounces is dispensed. The standard deviation of the process is 0.15 ounce. A sample of 50 bottles is selected periodically and the assembly line is stopped when there is evidence that the average amount dispensed is less than 8 ounces. Suppose that a sample of 50 bottles reveals an average of 7.983 ounces.

1. State the null and alternative hypotheses.

2. At the .05 level of significance, is there evidence that the average amount dispensed is less than 8 ounces?

A machine being used for packaging raisins has been set so that, on average, 15 ounces of raisins will be packaged per box. The operations manager wishes to test the machine setting and selects a sample of 30 consecutive raisin packages filled during the production process. The sample mean is 15.18 and the sample standard deviation is 0.4909. Use the t-distribution. Is there evidence that the mean weight per box is different from 15 ounces? (use level of significance equal to .05)

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