# EBook Problems

## Probability and Statistics EBook Practice Problems

The problems provided below may be useful for practicing the concepts, methods and analysis protocols, and for self-evaluation of learning of the materials presented in the EBook.

# I. Introduction to Statistics

## The Nature of Data and Variation

Although natural phenomena in real life are unpredictable, the designs of experiments are bound to generate data that varies because of intrinsic (internal to the system) or extrinsic (due to the ambient environment) effects. How many natural processes or phenomena in real life can we describe that have an exact mathematical closed-form description and are completely deterministic? How do we model the rest of the processes that are unpredictable and have random characteristics?

## Uses and Abuses of Statistics

Statistics is the science of variation, randomness and chance. As such, statistics is different from other sciences, where the processes being studied obey exact deterministic mathematical laws. Statistics provides quantitative inference represented as long-time probability values, confidence or prediction intervals, odds, chances, etc., which may ultimately be subjected to varying interpretations. The phrase Uses and Abuses of Statistics refers to the notion that in some cases statistical results may be used as evidence to seemingly opposite theses. However, most of the time, common principles of logic allow us to disambiguate the obtained statistical inference.

## Design of Experiments

Design of experiments is the blueprint for planning a study or experiment, performing the data collection protocol and controlling the study parameters for accuracy and consistency. Data, or information, is typically collected in regard to a specific process or phenomenon being studied to investigate the effects of some controlled variables (independent variables or predictors) on other observed measurements (responses or dependent variables). Both types of variables are associated with specific observational units (living beings, components, objects, materials, etc.)

## Statistics with Tools (Calculators and Computers)=

All methods for data analysis, understanding or visualizing are based on models that often have compact analytical representations (e.g., formulas, symbolic equations, etc.) Models are used to study processes theoretically. Empirical validations of the utility of models are achieved by inputting data and executing tests of the models. This validation step may be done manually, by computing the model prediction or model inference from recorded measurements. This process may be possible by hand, but only for small numbers of observations (<10). In practice, we write (or use existent) algorithms and computer programs that automate these calculations for better efficiency, accuracy and consistency in applying models to larger datasets.

# II. Describing, Exploring, and Comparing Data

## Types of Data

There are two important concepts in any data analysis - Population and Sample. Each of these may generate data of two major types - Quantitative or Qualitative measurements.

## Summarizing Data with Frequency Tables

There are two important ways to describe a data set (sample from a population) - Graphs or Tables.

## Pictures of Data

There are many different ways to display and graphically visualize data. These graphical techniques facilitate the understanding of the dataset and enable the selection of an appropriate statistical methodology for the analysis of the data.

## Measures of Central Tendency

There are three main features of populations (or sample data) that are always critical in understanding and interpreting their distributions - Center, Spread and Shape. The main measures of centrality are Mean, Median and Mode(s).

## Measures of Variation

There are many measures of (population or sample) spread, e.g., the range, the variance, the standard deviation, mean absolute deviation, etc. These are used to assess the dispersion or variation in the population.

## Statistics

Variables can be summarized using statistics - functions of data samples.

## Graphs and Exploratory Data Analysis

Graphical visualization and interrogation of data are critical components of any reliable method for statistical modeling, analysis and interpretation of data.

# III. Probability

## Fundamentals

Some fundamental concepts of probability theory include random events, sampling, types of probabilities, event manipulations and axioms of probability.

### Problems

1. In a large midwestern university with 30 different departments, the university is considering eliminating standardized scores from their admission requirements. The university wants to find out whether the students agree with this plan. They decide to randomly select 100 students from each department, send them a survey, and follow up with a phone call if they do not return the survey within a week. What kind of sampling plan did they use?

(a) Stratified random sampling
(b) Simple random sampling
(c) Multi-stage sampling
(d) Cluster sampling

2. It is believed that 5% of elementary school children have some kind of ADD (Attention Deficit Disorder). Researchers are hoping to track 60 or more of these students for several years. They decide to test 1500 first graders for this problem. What is the probability that they will find enough subjects for their study?

(a) Cannot be calculated with the given data
(b) More than 95%
(c) Less than 5%
(d) Between 70% to 80%

3. A box contains 6 balls, where 2 are red, 2 are white, and 2 are blue. Four balls are picked at random, one at a time. Each time a ball is picked, the color is recorded, and the ball is put back in the box. If the first 3 balls are red, what color is the fourth ball most likely to be?

(a) Red
(b) White
(c) Blue
(d) Blue and white are equally likely and more likely than red.
(e) Red, blue, and white are all equally likely.

4. A coin is tossed 400 times and 170 heads are observed. This coin is

(a) fair, because the probability of seeing that amount of heads or less is approximately 0.0013
(b) neither fair or unfair. There is not enough information to determine that.
(c) fair, because the probability of seeing that amount of heads or less is approximately 0.5
(d) not fair, because the probability of seeing that amount of heads or less is close to 0.

5. According to government data, 30% of single parents own a home. A study of the housing situation of single parents is based on a random sample of 400 single parents. What is the probability that the proportion of single parents owning a home in the sample is larger than 35%?

(a) 1.3
(b) 0.156
(c) 0.23
(d) None of the above

6. A fair coin is tossed, and it lands heads up. The coin is to be tossed a second time. What is the probability that the second toss will also be a head?

(a) 1/3
(b) 1/4
(c) Slightly less than 1/2
(d) Slightly more than 1/2
(e) 1/2

7. If a fair die is rolled eight times, which of the following ordered sequences of results, if any, is least likely to occur?

(a) 2 1 4 3 1 5 4 6
(b) 6 4 3 2 4 1 5 6
(c) 2 3 4 5 6 1 2 3
(d) All sequences are equally likely
(e) 5 6 2 6 3 5 4 2

8. When three fair dice are simultaneously thrown, which of the following results is most likely to be obtained?

(a) All three results are equally likely.
(b) A 5, a 3 and a 6 in any order
(c) Two 5's and a 3
(d) Three 5's

9. The probability model below describes the number of repair calls that an appliance repair shop may receive during an hour:

 Repair calls 0 1 2 3 P(x) 0.1 0.3 0.4 0.2

The probability that the number of repair calls is at least 2 is:

(a) 0.8
(b) 0.2
(c) 0.4
(d) 0.6

## Rules for Computing Probabilities

There are many important rules for computing probabilities of composite events. These include conditional probability, statistical independence, multiplication and addition rules, the law of total probability and the Bayesian rule.

### Problems

1. A professor who teaches 500 students in an introductory psychology course reports that 250 of the students have taken at least one introductory statistics course, and the other 250 have not taken any statistics courses. 200 of the students were freshmen, and the other 300 students were not freshmen. Exactly 50 of the students were freshmen who had taken at least one introductory statistics course.

If you select one of these psychology students at random, what is the probability that the student is not a freshman and has never taken a statistics course?

(a) 30%
(b) 40%
(c) 50%
(d) 60%
(e) 20%

2. A box contains 30 pens, where 5 are red, 14 are black, and 11 are blue. If you pick three pens from the box at random without replacement, what is the probability that these three pens will all be black?

(a) 14/30 + 14/30 + 14/30
(b) 14/30 + 13/29 + 12/28
(c) 14/30 x 13/29 x 12/28
(d) 1 - (14/30 x 13/29 x 12/28)

3. When three fair dice are simultaneously thrown, which of these three results is least likely to be obtained?

(a) All three results are equally unlikely.
(b) Two fives and a 3 in any order.
(c) A 5, a 3 and a 6 in any order.
(d) Three 5's.

4. Suppose that you take a three question "true/false" quiz for which you are completely unprepared. You have to guess the correct answer for each question. What is the probability of answering at least one question correctly?

(a) 4/8
(b) 5/8
(c) 7/8
(d) 1/8
(e) 3/8

5. Records show that in an introductory chemistry course in a college, 20% of the students get an A, 30% get a B, 40% get a C, and 10% get a D. If you pick three students at random, what is the probability that all three will get an A?

(a) 0.8*0.8*0.8
(b) 0.2*0.2*0.2
(c) 200*0.2*0.2*0.2
(d) 0.2*3

6.A newly born child is equally likely to be a boy or a girl. What is the probability that in a family of three children there are less than 3 boys?

(a) 0.125
(b) 0.75
(c) 0.875
(d) 0.5

7.A professor who teaches 300 students in an introductory psychology course reports that 135 of the students have taken exactly one introductory statistics course, 60 have taken two or more introductory statistics courses, and the other 105 have not taken any statistics courses. If you select one of these psychology students at random, what is the probability that the student has taken at least one statistics class?

(a) 0.20
(b) 0.45
(c) 0.65
(d) 0.35

8. Three fair coins are flipped. Find the probability that at least one comes up heads.

(a) 7/8
(b) 4/8
(c) 6/8
(d) 3/8
(e) 5/8

9. Two fair coins are flipped. The probability that both are heads is:

(b) Exactly 25%
(c) Exactly 12.5%
(d) Exactly 50%
(e) Exactly 75%

10. Two fair coins are flipped. The probability that the second coin is a head, given that the first was a head, is:

(a) Exactly 50%
(b) Exactly 25%
(c) Exactly 75%
(d) Exactly 12.5%

10. Three dice are rolled. The probability that at least one is a 5 is:

(a) 1/6 + 1/6 + 1/6
(b) 1/6 x 1/6 x 1/6
(c) 1 - (5/6 x 5/6 x 5/6)
(d) 5/6 + 4/6 + 3/6
(e) 5/6 x 4/6 x 3/6

## Probabilities Through Simulations

Many experimental setting require probability computations of complex events. Such calculations may be carried out exactly, using theoretical models, or approximately, using estimation or simulations.

### Problems

1. A certain soft drink company was having a promotional contest in which they claimed that 1 in 3 bottles contained a free download from an mp3 server. A professor noticed that one machine in the Math Sciences building gave him 8 free downloads in 11 purchases. If the company's claim is true, what is the probability of getting 8 or more free downloads in 11 purchases? We can design a simulation to find out.

The first step in a simulation is to identify the component to be repeated. Which of the choices below would be the best choice for the component to be repeated?

(a) The selection of 11 bottles of the soft drink.
(b) The selection of a bottle of the soft drink.
(c) The selection of 3 bottles of the soft drink.
(d) the selection of 8 bottles of the soft drink.

## Counting

There are many useful counting principles (including permutations and combinations) to compute the number of ways that certain arrangements of objects can be formed. This allows counting-based estimation of probabilities of complex events.

### Problems

1. Two cards are dealt to you (without replacement) from an ordinary well-shuffled deck. Let X = the probability that you have a pair. Let Y = the probability that both of your cards are diamonds. Compare X and Y.

(a) X < Y
(b) X = Y
(c) X > Y

# IV. Probability Distributions

## Expectation(Mean) and Variance)

1. Ming’s Seafood Shop stocks live lobsters. Ming pays $6.00 for each lobster and sells each one for$12.00. The demand X for these lobsters in a given day has the following probability mass function.

 X 0 1 2 3 4 5 P(x) 0.05 0.15 0.3 0.2 0.2 0.1

What is the Expected Demand?

(a) 13.5
(b) 3.1
(c) 2.65
(d) 5.2

2. If sampling distributions of sample means are examined for samples of size 1, 5, 10, 16 and 50, you will notice that as sample size increases, the shape of the sampling distribution appears more like that of the:

(a) normal distribution
(b) uniform distribution
(c) population distribution
(d) binomial distribution

# V. Normal Probability Distribution

## The Standard Normal Distribution

1. Weight is a measure that tends to be normally distributed. Suppose the mean weight of all women at a large university is 135 pounds, with a standard deviation of 12 pounds. If you were to randomly sample 9 women at the university, there would be a 68% chance that the sample mean weight would be between:

(a) 131 and 139 pounds.
(b) 133 and 137 pounds.
(c) 119 and 151 pounds
(d) 125 and 145 pounds.
(e) 123 and 147 pounds.

2. The amount of money college students spend each semester on textbooks is normally distributed with a mean of $195 and a standard deviation of$20. Suppose you take a random sample of 100 college students from this population. There is a 68% chance that the sample mean amount spent on textbooks is between:

(a) $193 and$197.
(b) $155 and$235.
(c) $191 and$199.
(d) $175 and$215.

3. A researcher converts 100 lung capacity measurements to z-scores. The lung capacity measurements do not follow a normal distribution. What can we say about the standard deviation of the 100 z-scores?

(a) It depends on the standard deviation of the raw scores
(b) It equals 1
(c) It equals 100
(d) It must always be less than the standard deviation of the raw scores
(e) It depends on the shape of the raw score distribution

4. The weights of packets of cookies produced by a certain manufacturer have a normal distribution with a mean of 202 grams and a standard deviation of 3 grams. What is the weight that should be stamped on the packet so that only 0.99% of packets are underweight?

(a) 200
(b) 195
(c) 190
(d) 205

5. GSP Inc. is trying two different marketing techniques for its toothpaste. In 20 test cities, it is using family branding. This sells toothpaste with a mean of 2,250 units per week and a standard deviation of 250 units per week. In 20 other test cities, GSP is using individual branding. This sells toothpaste with a mean of 2,250 units per week and a standard deviation of 500 units per week. GSP wants to select the marketing technique that sells at least 2,350 units per week more often. If the number of units sold per week follows a normal distribution, which marketing technique should GSP choose?

(a) Individual Branding
(b) Can't be answered with the information given
(c) Family Branding
(d) They each get the same result

6. Among first year students at a certain university, scores on the verbal SAT follow the normal curve. The average is around 500 and the SD is about 100. Tatiana took the SAT, and placed at the 85% percentile. What was her verbal SAT score?

(a) 604
(b) 560
(c) 90
(d) 403

7. A set of test scores are normally distributed. The mean is 100 and the standard deviation is 20. These scores are converted to z-scores. What are the z-scores of the mean and median?

(a) 1
(b) 100
(c) 0
(d) 50

8. In Japan there is an annual turkey dog eating contest. The number of turkey dogs that contestants eat are normally distributed with a mean of 36 turkey dogs and a standard deviation of 6 turkey dogs. A contestant eats 27 turkey dogs. What is his z-score?

(a) 6
(b) -1.5
(c) 9
(d) 1.5
(e) -9

# VI. Relations Between Distributions

## The Central Limit Theorem

1. Which of the following would make the sampling distribution of the sample mean narrower? Check all answers that apply.

(a) A smaller population standard deviation
(b) A smaller sample size
(c) A larger standard error
(d) A larger sample size
(e) A larger population standard deviation

## Normal Distribution as Approximation to Binomial Distribution

1. Under what condition will the approximation to the binomial distribution using the normal curve be most accurate?

(a) np>10 and n(1-p)>10
(b) Bernoulli trials for each member of the sample
(c) Dependence of the members of the sample.
(d) np>10 and n(1-p)<10

# VII. Point and Interval Estimates

## Estimating a Population Proportion

1. A 1996 poll of 1,200 African American adults found that 708 think that the American dream has become impossible to achieve. The New Yorker magazine editors want to estimate the proportion of all African American adults who feel this way. Which of the following is an approximate 90% confidence interval for the proportion of all African American adults who feel this way?

(a) (.56, .62)
(b) (.57, .61)
(c) Can't be calculated because the population size is too small.
(d) Can't be calculated because the sample size is too small.

2. True or False: In a well-designed sample survey like the Current Population Survey, the observed sample percentage (e.g, percentage unemployed) is equal to the population percentage. Thus, it is appropriate to just report the sample percentage, without any measure of accuracy (i.e. without the margin of error).

(a) True
(b) False

3. The BBC news does a story and at one point the reporter says: A polling agency reports that the percentage of the American public who agree we should spend more money on the mental health of the war veterans is 42% +/- 3%

(a) The probability that the American public agree that we should spend more money on the mental health of the war veterans is between 39% to 42%.
(b) The percentage of the American public who agree that we should spend more money on the mental health of the war veterans is between 39% to 45%.
(c) We are 95% confident that the percentage of the American public who agree that we should spend more money on the mental health of the war veterans is between 39% to 45%.
(d) The percentage of the American public who agree that we should spend more money on the mental health of the war veterans is 42%.

# VIII. Hypothesis Testing

## Fundamentals of Hypothesis Testing

1. Suppose you were hired to conduct a study to find out which of two brands of soda college students think taste better. In your study, students are given a blind taste test. They rate one brand and then rated the other, in random order. The ratings are given on a scale of 1 (awful) to 5 (delicious). Which type of test would be the best to compare these ratings?

(a) One-Sample t
(b) Chi-Square
(c) Paired Difference t
(d) Two-Sample t

2. USA Today's AD Track examined the effectiveness of the new ads involving the Pets.com Sock Puppet (which is now extinct). In particular, they conducted a nationwide poll of 428 adults who had seen the Pets.com ads and asked for their opinions. They found that 36% of the respondents said they liked the ads. Suppose you increased the sample size for this poll to 1000, but you had the same sample percentage who like the ads (36%). How would this change the p-value of the hypothesis test you want to conduct?

(a) No way to tell
(b) The new p-value would be the same as before
(c) The new p-value would be smaller than before
(d) The new p-value would be larger than before

3. A marketing director for a radio station collects a random sample of three hundred 18 to 25 year-olds and two hundred and fifty 25 to 40 year-olds. She records the percent of each group that had purchased music online in the last 30 days. She performs a hypothesis test, and the p-value of her test turns out to be 0.15. From this she should conclude:

(a) that about 15% more people purchased on-line music in the younger group than in the older group.
(b) there is insufficient evidence to conclude that there is a difference in the proportion of on-line music purchases in the younger and older group.
(c) the proportion of on-line music purchasers is the same in the under-25 year-old group as in the older group.
(d) the probability of getting the same results again is 0.15.

4. If we want to estimate the mean difference in scores on a pre-test and post-test for a sample of students, how should we proceed?

(a) We should construct a confidence interval or conduct a hypothesis test
(b) We should collect one sample, two samples, or conduct a paired data procedure
(c) We should calculate a z or a t statistic

5. The paint used to make lines on roads must reflect enough light to be clearly visible at night. Let mu denote the true average reflectometer reading for a new type of paint under consideration. A test of the null hypothesis that mu = 20 versus the alternative hypothesis that mu > 20 will be based on a random sample of size n from a normal population distribution. In which of the following scenarios is there significant evidence that mu is larger than 20?

(i) n=15, t=3.2, alpha=0.05

(ii) n=9, t=1.8, alpha=0.01

(iii) n=24, t=-0.2, alpha=0.01

(a) (ii) and (iii)
(b) (i)
(c) (iii)
(d) (ii)

6. The average length of time required to complete a certain aptitude test is claimed to be 80 minutes. A random sample of 25 students yielded an average of 86.5 minutes and a standard deviation of 15.4 minutes. If we assume normality of the population distribution, is there evidence to reject the claim? (Select all that applies).

(a) No, because the probability that the null is true is > 0.05
(b) Yes, because the observed 86.5 did not happen by chance
(c) Yes, because the t-test statistic is 2.11
(d) Yes, because the observed 86.5 happened by chance

7. We observe the math self-esteem scores from a random sample of 25 female students. How should we determine the probable values of the population mean score for this group?

(a) Test the difference in means between two paired or dependent samples.
(b) Test that a correlation coefficient is not equal to 0 (correlation analysis).
(c) Test the difference between two means (independent samples).
(d) Test for a difference in more than two means (one way ANOVA).
(e) Construct a confidence interval.
(f) Test one mean against a hypothesized constant.
(g) Use a chi-squared test of association.

8. Food inspectors inspect samples of food products to see if they are safe. This can be thought of as a hypothesis test where H0: the food is safe, and H1: the food is not A. If you are a consumer, which type of error would be the worst one for the inspector to make, the type I or type II error?

(a) Type I
(b) Type II

9. A college admissions officer is concerned that their admission criteria might not treat men and women with equal weight. To test this, the college took a random sample of male and female high school seniors from a very large local school district and determined the percent of males and females who would be eligible for admission at the college. Which of the following is a suitable null hypothesis for this test?

(a) p = 0.5
(b) The proportion of all eligible men in the district will not equal the proportion of all eligible women in the district.
(c) The proportion of all eligible men in the school district should be equal to the proportion of all eligible women in the school district.
(d) The proportion of eligible men sampled should equal the propotion of eligible women sampled.

## Testing a Claim About a Mean: Large Samples

1. Hong is a pharmacist studying the effect of an anti-depressant drug. She organizes a simple random sample of 100 patients, and then collect their anxiety test scores before and after administering the anti-depressant drug. Hong wants to estimate the mean difference between the pre-drug and post-drug test scores. How should she proceed?

(a) She should compute a confidence interval or conduct a hypothesis test
(b) She should calculate the z or the t statistics
(c) She should compute the correlation between the two samples
(d) Not enough information to tell

2. A utility company serves 50,000 households. As part of a survey of customer attitudes, they take a simple random sample of 750 of these households. The average number of television sets in the sample households turns out to be 1.86, and the standard deviation in the sample is 0.80. What sample size would be necessary for the standard error of the sample mean to be 0.02?

(a) 5,000
(b) 1,600
(c) 10,000
(d) 1,000

## Testing a Claim About a Mean: Small Samples

1. To test the claim that the average home in a certain town is within 5.5 miles of the nearest fire station, and insurance company measured the distances from 25 randomly selected homes to the nearest fire station and found x-bar = 5.8 miles and sd = 2.4 miles. Determine what the insurance company found out with a test of significance. Check all that apply.

(a) There is no evidence in the data to conclude that the distance is different from 5.5.
(b) The average of 5.8 miles observed is by chance.
(c) We cannot reject the null.
(d) There is evidence in the data to conclude that the distance is 5.5.

## Testing a Claim About a Proportion

1. A random sample of 1000 Americans aged 65 and older was collected in 1980 and found that 15% had "hazardous" levels of drinking, which is defined as regularly drinking an amount of alcohol that could cause health problems given the subject's medical conditions. Researchers wanted to know if this proportion has changed since 1980 and so collected a random sample of 1500 Americans aged 65 and older in 2004. They found that 12% drank at hazardous levels. Which of the following is closest to the value of a test statistic that could be used to test the hypothesis that the proportion of hazardous drinkers over the age of 65 has declined since 1980?

(a) -2.13
(b) 0.014
(c) 0.418
(d) 4.54

# X. Correlation and regression

## Correlation

1. A positive correlation between two variables X and Y means that if X increases, this will cause the value of Y to increase.

(a) This is always true.
(b) This is sometimes true.
(c) This is never true.

2. The correlation between high school algebra and geometry scores was found to be + 0.8. Which of the following statements is not true?

(a) Most of the students who have above average scores in algebra also have above average scores in geometry.
(b) Most people who have above average scores in algebra will have below average scores in geometry
(c) If we increase a student's score in algebra (ie. with extra tutoring in algebra), then the student's geometry scores will always increase accordingly.
(d) Most students who have below average scores in algebra also have below average scores in geometry.

3. Researchers discover that the correlation between miles ran per week and cardiovascular endurance is +0.75. They also discover that the correlation between hours spent watching television per week and cardiovascular endurance is -0.75. What is the conclusion that best characterizes the result of this study?

(a) Most people who spend a lot of hours watching television have low cardiovascular endurance.
(b) Most people who have good cardiovascular endurance spend a lot of time running and little time watching television.
(c) Based on the correlation, if you increase your running hours per week, your cardiovascular endurance will decrease.
(d) Based on the correlation, if you increases your television watching time, your cardiovascular endurance will decrease.
(e) Most people with a lot of miles ran per week have high cardiovascular endurance.

4. The correlation between working out and body fat was found to be exactly -1.0. Which of the following would not be true about the corresponding scatterplot?

(a) The slope of the best line of fit should be -1.0.
(b) All the points would lie along a perfect straight line, with no deviation at all.
(c) The best fitting line would have a downhill (negative) slope.
(d) 100% of the variance in body fat can be predicted from workout.

5. Suppose that the correlation between working out and body fat was found to be exactly -1.0. Which of the following would NOT be true, about the corresponding scatterplot?

(a) All points would lie along a straight line, with no deviation at all.
(b) 100% of the variance in body fat can be predicted from the workout.
(c) The slope of the linear model is -1.0.
(d) The best fitting line would have a negative slope.

6. A recent article in an educational research journal reports a correlation of +0.8 between math achievement and overall math aptitude. It also reports a correlation of -0.8 between math achievement and a math anxiety test. Which of the following interpretations is the most correct?

(a) You cannot compare a positive and a negative correlation.
(b) The correlation of +0.8 indicates a stronger relationship than the correlation of -0.8.
(c) The correlation of +0.8 is just as strong as the correlation of -0.8.
(d) It is impossible to tell which correlation is stronger.

7. Psychologists have shown that there is a relationship between stress levels and productivity. As stress levels increase, productivity also increases up to a certain point, and after that productivity decreases as stress levels increase. Suppose you were given this data for a random sample of 200 adults. If you calculated the Pearson coefficient of correlation, what would you expect to find?

(a) I would expect r to be between -0.50 to -0.70.
(b) I would expect r to be -1.
(c) I would expect r to be between 0.50 and 0.70.
(d) I would expect r to be +1.
(e) I would expect r to be zero.

8. If the correlation coefficient is 0.80, then:

(a) The explanatory variable is usually less than the response variable.
(b) The explanatory variable is usually more than the response variable.
(c) None of the statements are correct.
(d) Below-average values of the explanatory variable are more often associated with below-average values of the response variable.
(e) Below-average values of the explanatory variable are more often associated with above-average values of the response variable.

9. Given the following data, what is the best estimate for the coefficient of correlation between the ages of the husbands and wives?

There are 50 couples (husband and wife). The age range for men is from 50 to 70 years old. The age range for women is from 48 to 68 years old. For all of the couples, the husband is two years older than the wife. For instance, in one couple the husband is 50 years old and the wife is 48 years old.

(a) The coefficient of correlation between the age of husband and wife is equal to +1.
(b) We need the actual data to compute the coefficient of correlatin between the age of the husband and wife.
(c) The coefficient of correlation between the age of husband and wife is equal to zero.
(d) The coefficient of correlation between the age of husband and wife is equal to +0.50.
(e) The coefficient of correlation between the age of husband and wife is equal to -1.

## Regression

1. Use the information from the Heights of Fathers and Sons to write the linear model that best predicts the height of the son from the height of the father.

(a) Son's height = 35 + 0.5*Father's height'
(b) Son's height = 1.00 + 1.00* Father's height
(c) The model cannot be determined without the actual data
(d) Son's height = 0.5 + 35*Father's height

2. A congressional report investigates the relationship between income of parents and educational attainment of their daughters. Data are from a sample of families with daughters age 18-24. Average parental income is \$29,300, average educational attainment of the daughters is 13.1 years of schooling completed, and the correlation is 0.37.

The regression line for predicting daughter’s education from parental income is reported as: Predicted education = 0.000617*(income) + 8.1

Is the following statement true or false? "The above line is the regression line to predict education from income."

(a)True.
(b)False.

3. Heights of Fathers and Sons

In the early 1900's when Francis Galton and Karl Pearson measured 1078 pairs of fathers and their grown-up sons, they calculated that the mean height for fathers was about 68 inches with deviation of 3 inches. For their sons, the mean height was 69 inches with deviation of 3 inches. (The actual numbers are slightly smaller, but we will work with these values to keep the calculations simple.) The correlation coefficient was 0.50. Use the information to calculate the slope of the linear model that predicts the height of the son from the height of the father.

(a) 0.50
(b) The slope cannot be determined without the actual data
(c) 35.00
(d) 3/3 = 1.00

4. The National Highway Safety Administration is interested in the effect of seat belt use on saving lives. One study reported statistics on children under the age of 5 who were involved in motor vehicles accidents in which at least one fatality occurred. 7,060 such accidents between 1985 and 1989 were studied. Of those who survived, 1129 weren't wearing a seat belt, 432 were wearing an adult seat belt and 733 had a children's carseat belt. Of those with fatalities, 509 had no belt, 73 had an adult seat belt, and 139 had a children's carseat belt.

Are seat belt status and the outcome of the accidents independent?

(a) Yes
(b) No
(c) Can't tell with the information provided

5. Suppose that wildlife researchers monitor the local alligator population by taking aerial photograhs on a regular schedule. They determine that the best fitting linear model to predict weight in pounds from the length of the gators inches is:

Weight = -393 + 5.9*Length with r2 = 0.836.

Which of the following statements is true?

(a) A gator that is about 10 inches above average in length is about 59 pounds above the average weight of these gators.
(b) The correlation between a gator's length and weight is 0.836.
(c) The correlation between a gator's height and weight cannot be determined without the actual data.
(d) The correlation between a gator's height and weigth is about -0.914.

## Variation and Prediction Intervals

1. Two researchers are going to take a sample of data from the same population of physics students. Researcher A will select a random sample of students from among all students taking physics. Researcher B's sample will consist only of the students in her class. Both researchers will construct a 95% confidence interval for the mean score on the physics final exam using their own sample data. Which researcher's method has a 95% chance of capturing the true mean of the population of all students taking physics?

(a) Research B
(b) Researcher A
(c) Both methods have a 95% chance of capturing the true mean
(d) Neither

2. A random sample of 150 UCLA students found that 35% of the respondants wanted a elevator to replace Bruin Walk. A 95% confidence interval for the percentage of all UCLA students who feel this way is approximately:

(a) (24%, 46%)
(b) (32%, 38%)
(c) The sample size is too small to compute a confidence interval.
(d) (27%, 43%)

3. According to Terry Prachett, the short unit of time in the multiverse is the New York second, defined as the time interval between the light turning green and the cab behind you honking. A magazine took a poll of 100 New Yorkers and found that 90 people agree with that statement wholeheartedly. Which of the following is a 90% confidence interval for the proportion of people who agree with that statement?

(a) 0.9 +\- 0.50
(b) 0.9 +\- .05
(c) 0.9 +\- .03
(d) 0.9 +\- .06

4. A national poll found that 62% of all Americans agreed that more attention should be paid to mental health of war veterans. If a simple random sample of 326 people was used to make a 95% confidence interval of (0.57,0.67), what is the margin of error?

(a) 0.03
(b) 0.05
(c) 0.12
(d) In order to calculate the margin of error, we need the p-value of the population.

5. Hermione Granger is on a mission this year to complain about the astronomical cost of wizarding books to the Hogwart board of administrators. Given that the population mean for book cost is 10 and a standard deviation of 2 galleons, If Hermione were to take a simple random sample of 49 students and make a 68% confidence interval, what would be the range of values for the sample mean or Xbar?

(a) 8 and 12 galleons
(b) 9.4 and 10.6 galleons
(c) 6 and 14 Galleons
(d) 9.7 and 10.3 galleons

6. A 95% confidence interval indicates that:

(a) 95% of the intervals constructed using this process based on samples from this population will include the population mean
(b) 95% of the time the interval will include the sample mean
(c) 95% of the possible population means will be included by the interval
(d) 95% of the possible sample means will be included by the interval

7. Suppose we want to find out if a coin is not fair. To test this hypothesis we flip the coin 100 times, and in 63 out of 100 flips we get heads. We construct the confidence interval and find it to be (.53,.73). Interpret this confidence interval.

(a) 95 is the Z score that corresponds to our distribution of sample means
(b) Confidence is something you learn at fraternity parties
(c) 95% of the time the true proportion of flips that are heads is between .53 and .73
(d) If we were to repeat this expirement over and over again, 95 times out of 100 our Confidence interval would cover the true proportion of flips that are heads

8. A 95% confidence interval is calculated for a sample of weights of 100 randomly selected pigs, and is (42 pounds, 48 pounds). Will the sample mean weight fall within the confidence interval?

(a) Yes
(c) No

9. The average number of fruit candies in a large bag is estimated. The 95% confidence interval is (40, 48). Based on this information, you know that the best estimate of the population mean is:

(a) 43
(b) 40
(c) 45
(d) none of the above.
(e) 44

10. Suppose we plan to take a random sample of adults in the U.S. and determine the percent of them who have attended church in the last 30 days. We calculate a 90% confidence interval for the proportion of all adults in the U.S. who attended church in the last 30 days. Which of the following changes in our plans would result in a wider confidence interval? Check all that apply.

(a) Using an 85% confidence level.
(b) Using a 95% confidence level.
(c) Using a larger sample.
(d) Using a smaller sample.

11. Kevin has always, ever since he was a wee lad, wondered what proportion of the candies in M&M chocolate candies bags are yellow. However, his persistent calls to the M&M headquarter were of no avail. Now that he wields the awesome power of being a TA for Stat 10, he makes each of his 200 students go buy a M&M bag, count the colors, and compute a 99% confidence intervals for the yellow candy proportion. Assume that each M&M bag is a random sample, approximately how many of the 200 confidence intervals will not capture the true population proportion for yellow M&M's?

(a) Not enough information for an answer
(b) 0 to 4
(c) 4 to 8
(d) 12 to 14
(e) 8 to 12

12. A 95% confidence interval for the proportion of U.S. adults who favor the death penalty is given by (0.03, 0.09). Is the following statement true or false?

"There is a 95% probability that an adult in the US is in favor of the death penalty."

(a) True
(b) False