Question 1
Question
A local corporation was interested in the purchasing habits of Wake County residents.Specifically one of the things they were interested in was the proportions of residents that did a major home improvement project in the last year.The corporation used a list of all households to take a simple random sample of households.The researcher then visited each of the sampled homes and found that 21 of 100 homes had completed a major home improvement project.
Which of the following are true?
Select one or more:
Answer

The parameter of interest is the 100 homes that were sampled.

The population of interest is all Wake County residents.

The parameter of interest is 21%.

The population of interest is all Wake County residents who had completed a major home improvement project.

The parameter of interest is all Wake County residents.

The population of interest is the 100 homes that were sampled.

The population of interest is all Americans.

The parameter of interest is the proportion of residents that did a major home improvement project in the last year.
Question 2
Question
Online website surveys such as “quick votes”
Select one or more:
Answer

often reflect the opinions of those with strong opinions.

are examples of stratified sampling.

are examples of volunteer response sampling.

are examples of cluster sampling
Question 3
Question
The state Department of Public Instruction (DPI) would like to sample high school mathematics teachers to complete a survey on teaching methods. Among high school teachers some are National Board Certified (NBC) Teachers and some are not. A researcher compiled a list of all high school mathematics teachers in the state and divide the list into NBC teachers and nonNBC teachers. She then numbered these two lists and use a random number generator to pick 50 NBC teachers and 50 nonNBC teachers. This sample is best described as
Select one:
Answer

A cluster sample with two clusters (NBC and nonNBC teachers).

A volunteer response sample since teachers choose if they become NBC.

A stratified sample stratified on NBC status.

A simple random sample since all teachers have an equal chance of being chosen.
Question 4
Question
A researcher wants to find out how college students feel about the Social Security system. Which of the following unbiased methods could the researcher use?
Select one or more:
Answer

The researcher places a poll question on the main university website and allow students to vote whether or not they like the system.

The researcher takes a random sample from the enrollment list of the college and emails the survey to the selected students.

The researcher sets up a booth outside of the large classroom building and ask students to fill out a survey as they pass.

The researcher places a survey in the campus paper which students could cut out and mail to the researcher.

The researcher randomly selects 10 classes and asks all the students in those classes to fill out an anonymous survey.
Question 5
Question
In a recent survey several individuals could not be found even after three attempts to contact them. This is an example of:
Select one:
Answer

a. Response bias

b. Selection bias

c. Nonresponse bias

d. Undercoverage
Question 6
Question
The student government at the University of Missouri conducted a survey of the university's students. Three hundred (300) of the 26,000 students were contacted and asked if there was a need for an additional parking garage on campus. Of the 300 students contacted 23% said an additional garage was needed. Which of the following would possibly be an example of undercoverage?
Select one:
Answer

a. The survey was taken using the campus directory (which does not contain all students) as a sampling frame.

b. When the data recorded was recorded some answers were incorrectly entered into the computer.

c. Some students did not want to answer the questions asked.

d. The wording of the question was very confusing to some students.
Question 7
Question
Does daily exposure to bright light make subjects more alert? A study was conducted in which the daily habits of 30 college students were documented, focusing on how much time they spent in brightly lit rooms or outside on sunny days.After a week, the subjects were given a computerbased alertness test on which they receive a score on a 0 to 100 point scale.Their scores were compared with how much time they spent in brightly lit places that week.
Select one or more:
Answer

This study is best described as an experiment.

The response variable is how much time the students spent in brightly lit places.

The explanatory variable is how much time the students spent in brightly lit places.

The response variable is the score on the computerbased test.

The explanatory variable is the score on the computerbased test.

This is best described as an observational study.
Question 8
Question
About 870 men took part in a study to study the effectiveness of a hormone therapy. Half of the men were selected randomly to come in and receive the hormone therapy while the other half were told to stay home and thus did not receive the therapy. After about a year, blood tests were conducted on each subject by a lab technician who was aware of which group (treatment or those given nothing) the blood samples originated from. In presenting the results of the experiment, the authors reported that the men in the treatment group had experienced a statistically significant increase in HDL (the socalled "good" cholesterol) and a statistically significant reduction in LDL (the socalled "bad" cholesterol) when compared with the control group.
Select one or more:
Answer

This is an example of a completely randomized design.

This study would be classified as doubleblind.

This is an example of a block design.

The subjects are the blood tests.

The subjects are the 870 men in the study.

The treatments are the HDL and the LDL.

This study would be classified as unblinded.

This study would be classified as singleblind.

The treatments are the hormone therapy or the absence of it.

This is an example of a matched pairs design.
Question 9
Question
A researcher wants to test how diets A and B affect the weight loss of rabbits. She has 20 rabbits to use, but all of the rabbits are different sizes, which might affect how much weight they lose. The researcher decides to group the four smallest rabbits in one group, the next four smallest rabbits in another group, etc., until the final group has the four largest rabbits. Then, from each group she randomly selects two rabbits to have diet A, and the remaining rabbits in the groups have diet B.
Select one or more:
Answer

The treatment is how much weight a rabbit loses.

This is an example of a matched pairs experiment.

This is an example of a completely randomized experiment.

This is an example of a block design.

The subjects are diets A and B.

The subjects are the 20 rabbits.

The treatments are diets A and B.
Question 10
Question
An experiment that claimed to show that meditation reduces anxiety proceeded as follows. The experimenter interviewed the subjects and rated their anxiety. The subjects were then randomly assigned to two groups. The experimenter taught one group how to meditate, and they meditated daily for a month. The other group was simply told to relax more. At the end of the month, the experimenter interviewed all the subjects again and rated their anxiety levels. The meditation group had less anxiety. This study was criticized for not being blinded. What does ‘not blinded’ mean?
Select one:
Answer

The subjects in the control group did not take a placebo.

There is no real control group since one group was taught to meditate and the other group was told to relax more.

Anxiety is hard to quantify and the rater who reviewed their anxiety level may give different ratings than other raters.

The experimenter who was rating the subjects knows whether they were in the meditation group or not.
Question 11
Question
In research studies the placebo effect
Select one:
Answer

influences the group that gets a placebo.

influences neither the group that gets the placebo nor the group that gets the real treatment.

influences the group that gets the real treatment.

influences both the group that gets the placebo and the group that gets the real treatment.
Question 12
Question
The school committee of a small town surveys every family in the town and records X = {the number of children in each household}. Based on this data, they calculate E(X) = 2.2. Select the best interpretation of the expected value in this context.
Select one:
Answer

a. The most common number of children in a household is 2.2.

b. Each household has 2.2 children.

c. We cannot interpret this value without knowing the distribution of X.

d. We would expect 2.2 children, on average, for each household.
Question 13
Question
Use the following for questions 13  15
Let X be a continuous random variable with distribution:
f(x) = (1/10) + (x/5) for 1 <= x <= 3
What is the cumulative distribution function of X?
Select one:
Question 14
Question
Use the following for questions 2 to 4.
Let X be a continuous random variable with distribution:
f(x) = (1/10) + (x/5) for 1 <= x <= 3
Calculate P(1.7 < X < 2.2).
Round your answer to 3 decimal places and do not include any symbols other than a decimal point.
Answer: [blank_start]0.245[blank_end]
Question 15
Question
Use the following for questions 2 to 4.
Let X be a continuous random variable with distribution:
f(x) = (1/10) + (x/5) for 1 <= x <= 3
Calculate the expected value of X.
Round your answer to 3 decimal places and do not include any symbols other than a decimal point or negative sign, if necessary.
Answer: [blank_start]2.133[blank_end]
Question 16
Question
Suppose 20% of all purchases at a particular online store are made with PayPal. Let X = the number of purchases made at this store with PayPal out of 15 randomly selected purchases. [Note: the fact that the purchases were randomly selected implies they will be independent.]
What is the probability that exactly 4 purchases are made with PayPal at this store?
Give your answer to 4 decimal places. Do not include symbols other than a decimal point.
Answer: [blank_start]0.1876[blank_end]
Question 17
Question
Suppose 20% of all purchases at a particular online store are made with PayPal. Let X = the number of purchases made at this store with PayPal out of 15 randomly selected purchases. [Note: the fact that the purchases were randomly selected implies they will be independent.]
Consider the previous problem. How many purchases at this store would we expect to be made with PayPal?
Answer: [blank_start]3[blank_end]
Question 18
Question
After taking an aptitude test, the computer told Bob that he had a zscore of 1.08.
If scores on the aptitude test are normally distributed, which of the following statements can Bob conclude from his score?
Select one or more:
Answer

Bob scored within 1 standard deviation of the mean score.

Bob did worse than the mean score.

About 14% of students taking the aptitude test did worse than Bob.

Bob scored within 2 standard deviations of the mean score.

About 14% of students taking the aptitude test did better than Bob.

Bob did better than the mean score.
Question 19
Question
The Mental Development Index (MDI) of the Bayley Scales of Infant Development is a standardized measure used in longitudinal followup of highrisk infants. The scores on the MDI have approximately a normal distribution with a mean of 100 and standard deviation of 15. What proportion of children have MDI of at least 88?
Select one:
Question 20
Question
A state administered standardized reading exam is given to eighth grade students. The scores on this exam for all students statewide have a normal distribution with a mean of 502 and a standard deviation of 43. A local Junior High principal has decided to give an award to any student who scores in the top 10% of statewide scores.
How high should a student score be to win this award?
Report your answer to 2 decimal places.
Answer: [blank_start]557.11[blank_end]
Question 21
Question
A continuous random variable X is said to have a uniform distribution if the pdf of X is:
f(x) = 1 / (ba) for a < X < b
Show that f(x) is a valid probability distribution and use the definition of expected value to derive a form for the mean of X
[blank_start]E(X) = (b+a)/2[blank_end]
Question 22
Question
An instructor in a college class recently gave an exam that was worth a total of 100 points. The instructor inadvertently made the exam harder than he had intended. The scores were very symmetric, but the average score for his students was 54 and the standard deviation of the scores was 4 points. The instructor is considering 2 different strategies for rescaling the exam results:
Method 1: Add 20 points to everyone's score.
Method 2: Multiply everyone's score by 1.5.
Select one:
Answer

a. Method 2 will increase the standard deviation of the students’ scores.

b. Method 1 will increase the standard deviation of the students’ scores.

c. Method 1 will decrease the standard deviation of the students’ scores.

d. Both a and b, but not c.
Question 23
Question
A large multinational company knows that the average age of their employees is 34 years. They also know that the standard deviation of the ages of these employees is 8 years. We know that the population of employee ages will have a right skewed distribution. A manager from human resources is going to randomly select a sample of 100. Which of the following is true?
Select all that apply.
Select one or more:
Answer

We know that the shape of the sampling distribution of the mean will be approximately symmetric.

The sampling distribution of the mean will have the same standard deviation as the population.

The sampling distribution of the mean will have a smaller standard deviation than the population.

We can not tell what the shape sampling distribution of the mean will look like.

The sampling distribution of the mean will have a larger standard deviation than the population.

We know that the shape of the sampling distribution of the mean will be right skewed.
Question 24
Question
From census data it is known that the average income of households in Wake County is $58,500. It is also known that the distribution of household income in Wake County is strongly skewed to the right with a standard deviation of $14,000. A researcher is going to randomly select a sample of 5 households from Wake County. Which of the following is true?
Select all that apply.
Select one or more:
Answer

The sampling distribution of the mean will have a smaller standard deviation than the population.

We know that the shape of the sampling distribution of the mean will be right skewed.

We can not tell what the shape sampling distribution of the mean will look like.

The sampling distribution of the mean will have the same standard deviation as the population.

We know that the shape of the sampling distribution of the mean will be approximately symmetric.

The sampling distribution of the mean will have a larger standard deviation than the population.
Question 25
Question
The Mental Development Index (MDI) of the Bayley Scales of Infant Development is a standardized measure used in longitudinal followup of highrisk infants. The scores on the MDI have approximately a normal distribution with a mean of 100 and standard deviation of 16. We are going to randomly select 64 children and average their MDI scores. What is the probability that the average is under 105?
Give your answer to 4 decimal places.
Answer: [blank_start]0.9938[blank_end]
Question 26
Question
In engineering and product design, it is important to consider the weights of people so that airplanes or elevators aren't overloaded. Based on data from the National Health Survey, we can assume the weight of adult males in the US has a mean weight of 177 pounds and standard deviation of 32 pounds. We randomly select 50 adult males. What is the probability that the average weight of these 50 adult males is over 190 pounds?
Give your answer to 4 decimal places.
Answer: [blank_start]0.0021[blank_end]
Question 27
Question
A fastfood restaurant operates both a drivethrough facility and a walkin facility. On a randomly selected day, let X = the proportion of the time the drivethrough facility is in use and let Y = the proportion of the time the walkin facility is in use. Suppose that the joint distribution of X and Y is
f(x,y)=(2/3)(x+2y) for 0<x<1 and 0<y<1
What proportion of the time is the drivethrough facility expected to be in use?
Answer

0.611

0.333

0.417

0.376

0.556

0.125
Question 28
Question
A fastfood restaurant operates both a drivethrough facility and a walkin facility. On a randomly selected day, let X = the proportion of the time the drivethrough facility is in use and let Y = the proportion of the time the walkin facility is in use. Suppose that the joint distribution of X and Y is
f(x,y)=(2/3)(x+2y) for 0<x<1 and 0<y<1
What is the probability that the drivethrough facility and the walkin facility are each in use less than half of the time?
Select one:
Answer

0.417

0.611

0.125

0.376

0.333

0.556
Question 29
Question
Consider three independent random variablesX, Y, and Z, such that
E(X) = 6, V(X) = 2
E(Y) = 10, V(Y) = 5
E(Z) = 3, V(Z) = 1
Calculate E(2X + Y  3Z).
Select one:
Question 30
Question
Consider three independent random variablesX, Y, and Z, such that
E(X) = 6, V(X) = 2
E(Y) = 10, V(Y) = 5
E(Z) = 3, V(Z) = 1
Calculate V(2X + Y  3Z).
Select one:
Question 31
Question
Suppose that in a certain examination procedure, candidates must take two tests. Let X1 measure the score of a candidate on test 1 and X2 measure the score of a candidate on test 2. Further, suppose that scores on test 1 are distributed with a mean of 18 and a variance of 24 points, while scores on test 2 are distributed with a mean of 30 and a variance of 60 points.
An examination board wishes to calculate a final score for each candidate that is a weighted average these two test scores using the following formula:
Y = (2/3)*X1 + (1/3)*X2
Based on this information, which of the following is true?
Select one or more:
Answer

The variance of the final scores is 36 points.

Since X1 and X2 are likely dependent, we do not have enough information to calculate the variance of the final scores.

Since X1 and X2 are likely dependent, we do not have enough information to calculate the expected value of the final scores.

The variance of the final scores is 17.3 points.

The expected value of the final scores is 22 points.

The expected value of the final scores is 11.3 points.
Question 32
Question
Which of the following are true?
Select one or more:
Answer

The tdistribution is skewed to the right.

The tdistribution is symmetric.

The tdistribution is centered at 1.0

The tdistribution is centered at 0.

The tdistribution has more values at the extremes than a standard normal distribution.

The tdistribution has fewer values at the extremes than a standard normal distribution
Question 33
Question
df=10, 90% confidence [blank_start]Answer 1[blank_end]
df=16, 80% confidence [blank_start]Answer 2[blank_end]
df=2, 99% confidence [blank_start]Answer 3[blank_end]
df=4, 98% confidence [blank_start]Answer 4[blank_end]
Answer

1.812

1.337

9.925

3.747

1.812

1.337

9.925

3.747

1.812

1.337

9.925

3.747

1.812

1.337

9.925

3.747
Question 34
Question
The director of student health at a small high school is studying how many calories students at her high school consume in a day. She asks the first 40 students who come to the health room how many calories they consume in a 24 hour period and records the results. From the sample she found the average number of calories consumed was 1851 and that the standard deviation was 350. However before she finds the confidence interval for how many calories students consume in one day she goes to the statistics teacher for advice. What should the statistics teacher's advice be?
Select one or more:
Answer

The Central Limit does not apply because the sample is not random.

The standard devaition is not large enough to compute the confidence interval.

She can calculate the confidence interval but should use a tdistribution since it deals with an average.

The population may not be normal, but the Central Limit Theory applies, Thus she should compute the confidence interval as normal.

She did not take a simple random sample of the students, thus she should not compute the confidence interval.
Question 35
Question
We would like to create a confidence interval. Which of the following would produce the smallest margin of error?
Select one:
Answer

A 99% confidence level and a sample size of 50 subjects.

A 90% confidence level and a sample size of 300 subjects.

A 90% confidence level and a sample size of 50 subjects.

A 99% confidence level and a sample size of 300 subjects.
Question 36
Question
In creating confidence intervals for the mean with 95% confidence we have about 5% of the possible intervals that will miss the true population parameter. Why do some of the intervals miss the true parameter?
Select one
Answer

Because the parent population is skewed and about 5% of the distribution is in the tail of the distribution.

Because the standard deviation of the sample is about 5% smaller than the population standard deviation.

Because some samples are taken in an incorrect way and we know from experience that this happens about 5% of the time.

Because about 5% of possible samples lead to a statistic in the extreme tails of the sampling distribution.
Question 37
Question
We should be wary of a poll that has a high nonresponse rate because
Select one:
Answer

a. those who refused to respond may be different from those who participate.

b. the sampling frame must not have been representative of the population.

c. the margin of error will be very large.

d. the mean and median will be different because the results are skewed.
Question 38
Question
An administrator with the Missouri State Board of Education would like to determine the proportion of graduating seniors in the state that have been accepted into college for the next year. They would like to take a random sample of at least 1000 subjects.
What is the parameter of interest in this situation?
Select one:
Answer

All graduating seniors.

The 1000 subjects.

The proportion of the sampled subjects that have been accepted into college for the next year.

The proportion of all graduating seniors in Missouri that have been accepted into college for the next year.
Question 39
Question
A crop scientist is conducting research with a drought resistant corn hybrid. She is interested in determining if increasing the spacing between these plants will increase plant height. She prepares 20 single acre plots and randomly assigns 10 to have normal spacing while the other 10 are planted with an expanded spacing. The resulting average height for each group of 10 plots was recorded.
Select all that apply.
Select one or more:
Answer

This study is best described as an experiment.

The response variable is whether or not the plants have normal or expanded spacing.

The explanatory variable is the average height for each group of 10 plots.

This is best described as an observational study.

The response variable is the average height for each group of 10 plots.

The explanatory variable is whether or not the plants have normal or expanded spacing.
Question 40
Question
Let X be a continuous random variable with Cumulative Density Function (CDF)
F(x)=1 1/[(x+1)^(2)]
for x > 0. What is P(1 < X < 2)?
Select one:
Question 41
Question
A forestry researcher wants to estimate the average height of trees in a forest near Atlanta, Georgia. She takes a random sample of 18 trees from this forest. The researcher found that the average height was 4.8 meters with a standard deviation of 0.55 meters. Assume that the distribution of the heights of these trees is normal. For this sample what is the margin of error for her 99% confidence interval?
Give your answer to 3 decimal places.
Answer: [blank_start]0.376[blank_end]
Question 42
Question
A survey of undergraduates at NCSU asked a random sample of 80 students about the amount they had spent on textbooks (in dollars) during the current term. The 95% confidence interval created from this data was $375 ± $35. Which of the following statements are true?
Answer

$35 is 95% of the true average for all students.

We estimate that, in 95% of the possible samples from this population, the sample average will be within $35 of the true average.

95% of all students at this university spent between $340 and $410 on textbooks this term.

We are 95% confident that the true average is between $340 and $410.

95% of the possible confidence intervals (based on random samples of 80 students) will contain the true average.
Question 43
Question
It is reported that 30% of all pipework failures in chemical plants are caused by operator error; suppose this is the true probability p of a pipework failure being caused by operator error.
Calculate the probability that 6 out of a random sample of 10 pipework failures would be caused by operator error.
Report your answer to 4 decimal places.
Answer: [blank_start]0.0368[blank_end]
Question 44
Question
An elementary school teacher wanted to determine if one song about a certain history topic would improve students' understanding of the topic over another song. A teacher had 24 students in her class, and she randomly assigned 12 students to learn the first song, and 12 students to learn the second song. The next day the teacher gave the students a test on the history topic.
This study would best be described as
Select one: