blue packet MC

Employees at a large company can earn monthly bonuses. The distribution of monthly bonuses earned by all employees last year has mean 2.3 and standard deviation 1.3. Let z represent the standard normal distribution. If x represents the mean number of monthly bonuses earned last year for a random sample of 40 employees, which of the following calculations will give the approximate probability that x is less than 2 ?

A

A sample of 942 homeowners are classified, in the two-way frequency table below, by the number of credit cards they have and the number of years they have owned their current homes. text... Of the homeowners in the sample who have four or more credit cards, what proportion have owned their current homes for at least one year? A 78/212 B 78/258 C 78/942 D 212/942 E 258/942

A 78/212

A carnival game allows the player a choice of simultaneously rolling two, four, six, eight, or ten fair dice. Each die has six faces numbered 1 through 6, respectively. After the player rolls the dice, the numbers that appear on the faces that land up are recorded. The player wins if the greatest number recorded is 1 or 2. How many dice should the player choose to roll to maximize the chance of winning? A Two B Four C Six D Eight E Ten

A Two

In a national study on transportation patterns, 1,000 randomly selected adults will be asked the question: How many trips per week do you make to the grocery store? The sample mean will be computed. Let µ denote the population mean response to the question if everyone in the population is to be asked the question. Is the sample mean x unbiased for estimating µ? A Yes, because for random samples the mean (expected value) of the sample mean x is equal to the population mean µ. B Yes, because with a sample size of 1,000 the standard deviation of the sample mean x is small. C Yes, because the wording of the question is not biased. D No, because the sample mean x does not always equal the population mean µ. E No, because number of trips to the grocery story is not normally distributed so the mean (expected value) of the sample mean x does not equal the population mean µ.

A Yes, because for random samples the mean (expected value) of the sample mean x is equal to the population mean µ.

The p-value for a one-sided t-test is 0.10. If the test had been two-sided, what would the p-value have been? A 0.05 B 0.20 C 0.90 D 0.95 E It depends on the direction of the alternative hypothesis.

B 0.20

The distribution of colors of candies in a bag is as follows. text... If two candies are randomly drawn from the bag with replacement, what is the probability that they are the same color? A 0.09 B 0.22 C 0.25 D 0.75 E 0.78

B 0.22

For flights from a particular airport in January, there is a 30 percent chance of a flight being delayed because of icy weather. If a flight is delayed because of icy weather, there is a 10 percent chance the flight will also be delayed because of a mechanical problem. If a flight is not delayed because of icy weather, there is a 5 percent chance that it will be delayed because of a mechanical problem. If one flight is selected at random from the airport in January, what is the probability that the flight selected will have at least one of the two types of delays? A 0.065 B 0.335 C 0.350 D 0.450 E 0.665

B 0.335

A statistics teacher wants to determine whether there is a linear relationship between high school students' heights, in inches (in), and the lengths of their feet, in centimeters (cm). The teacher obtains height and foot-length measurements for a random sample of 23 students at the high school and generates the following graph and computer output. text... text... Provided that the assumptions for regression inference are satisfied, which of the following provides a 95 percent confidence interval estimate of the slope of the population regression line for predicting foot length from height?

B 0.583 ± (2.080) (0.138)

A survey was administered to parents of high school students in a certain state to see if the parents thought the students' academic needs were being met. To select the sample, the parents were divided into two groups— one group of parents who live in cities with populations of more than 100,000 and the other group of parents who live in cities with populations less than or equal to 100,000. A random sample of 100 parents from each group was taken. Which of the following statements about the sample of 200 parents is true? A It is a convenience sample because the sample of parents was easily obtained. B It is a stratified random sample because parents were randomly selected from each group. C It is a random cluster sample because parents were randomly selected from each group. D It is a random cluster sample because groups of high schools were randomly selected. E It is a systematic sample because the parents were systematically divided into two groups.

B It is a stratified random sample because parents were randomly selected from each group.

In a large set of data that are approximately normally distributed, r is the value in the data set that has a z-score of -1.00 s is the value of the first quartile, and t is the value of the 20th percentile. Which of the following is the correct order from least to greatest for the values of r, s, and t ? A r, s, t B r, t, s C s, t, r D t, r, s E t, s, r

B r, t, s

Approximately 52 percent of all recent births were boys. In a simple random sample of 100 recent births, 49 were boys and 51 were girls. The most likely explanation for the difference between the observed results and the expected results in this case is A bias B variability due to sampling C nonsampling error D a sampling frame that is incomplete E confounding

B variability due to sampling

A random sample of 300 students is selected from a large group of students who use a computer-equipped classroom on a regular basis. Occasionally, students leave their USB drive in a computer. Of the 300 students questioned, 180 said that they write their name on their USB drive. Which of the following is a 98 percent confidence interval for the proportion of all students using the classroom who write their name on their USB drive?

C

Let X be a random variable whose values are the number of dots that appear on the uppermost face when a fair die is rolled. The possible values of X are 1, 2, 3, 4, 5, and 6. The mean of X is 7/2 and the variance of X is 35/12. Let Y be the random variable whose value is the difference (first minus second) between the number of dots that appear on the uppermost face for the first and second rolls of a fair die that is rolled twice. What is the standard deviation of Y ?

C

Mating eagle pairs typically have two baby eagles (called eaglets). When there are two eaglets, the parents always feed the older eaglet until it has had its fill, and then they feed the younger eaglet. This results in an unequal chance of survival for the two eaglets. Suppose that the older eaglet has a 50 percent chance of survival. If the older eaglet survives, the younger eaglet has a 10 percent chance of survival. If the older eaglet does not survive, the younger eaglet has a 30 percent chance of survival. Let X be the number of eaglets that survive. Which of the following tables shows the probability distribution of X ?

C

Which of the following distinguishes an observational study from a randomized experiment? A In an observational study volunteers are always used, whereas in a randomized experiment a random sample is always taken from the population. B In an observational study a random sample is always taken from the population, whereas in a randomized experiment volunteers are always used. C In an observational study treatments are not randomly assigned, whereas in a randomized experiment treatments are randomly assigned. D In an observational study a control group is never used, whereas in a randomized experiment a control group is always used. E An observational study can be double-blind, whereas a randomized experiment can only be single-blind because the experimenter determines who is randomly assigned to each treatment.

C In an observational study treatments are not randomly assigned, whereas in a randomized experiment treatments are randomly assigned.

A scatterplot of student height, in inches, versus corresponding arm span length, in inches, is shown below. One of the points in the graph is labeled A. text... If the point labeled A is removed, which of the following statements would be true? A The slope of the least squares regression line is unchanged and the correlation coefficient increases. B The slope of the least squares regression line is unchanged and the correlation coefficient decreases. C The slope of the least squares regression line increases and the correlation coefficient increases. D The slope of the least squares regression line increases and the correlation coefficient decreases. E The slope of the least squares regression line decreases and the correlation coefficient increases.

C The slope of the least squares regression line increases and the correlation coefficient increases.

A large clinical trial was designed to determine whether a certain vitamin improves the general health of adults. The investigators first identified 85 variables that measure various aspects of the general health of adults. Because each adult in the clinical trial was to serve as his or her own control, the 85 variables were measured for each adult, both before taking the vitamin and after taking the vitamin for three months. The investigators then performed 85 matched-pair t-tests, one for each variable. They found statistically significant results at the 0.05 level in 2 of the variables, both in the direction of improved general health. Which of the following should the investigators conclude? A There is evidence that the vitamin improves the health of adults because 2 of the 85 tests were statistically significant. B There is evidence that the vitamin improves the health of adults because in clinical trials investigators typically underestimate the proportion of the population that is helped by a vitamin. C There is insufficient evidence that the vitamin improves the health of adults because at the 0.05 significance level, one could easily get statistically significant results in 2 out of 85 tests just due to chance variability. D There is insufficient evidence that the vitamin improves the health of adults because the sample size of 85 is not large enough to draw a conclusion. E No conclusion can be drawn because an even number of variables is needed for a matched-pairs design.

C There is insufficient evidence that the vitamin improves the health of adults because at the 0.05 significance level, one could easily get statistically significant results in 2 out of 85 tests just due to chance variability.

Administrators at a state university computed the mean GPA (grade point average) for juniors and seniors majoring in either physics or chemistry. The results are displayed in the table below. When juniors and seniors are grouped together, could physics majors have a higher mean GPA than chemistry majors? text... A No. The physics majors' mean GPA for juniors and seniors must be 3.0, while the chemistry majors' mean GPA for juniors and seniors must be 3.3. B No. There is not enough information to determine the mean GPA for each major, but it must be higher for chemistry majors than for physics majors. C Yes. It could happen. Whether it does happen depends on the number of juniors and seniors in each major. D Yes. It could happen. Whether it does happen depends on the variability of the GPAs within each of the four groups of students. E Yes. It could happen. Whether it does happen depends on the shapes of the distributions of the GPAs for each of the four groups of students.

C Yes. It could happen. Whether it does happen depends on the number of juniors and seniors in each major.

A distribution of scores is approximately normal with a mean of 78 and a standard deviation of 8.6. Which of the following equations can be used to find the score x above which 33 percent of the scores fall?

D

Which of the following histograms could have been constructed from the same set of data summarized by the boxplot above?

D

The manager of a car company will select a random sample of its customers to create a 90 percent confidence interval to estimate the proportion of its customers who have children. Of the following, which is the smallest sample size that will result in a margin of error of no more than 6 percentage points? A 100 B 125 C 150 D 200 E 275

D 200

An amateur men's swimming association is trying to decide whether times in the 100-meter breaststroke will be reduced if the men shave their heads. From the population of swimmers, six were selected at random and agreed to swim two races—one before shaving their heads and one after shaving their heads. The results for each race, with times in seconds, are given in the table below. text... Let µ1 represent the population mean of swimming times before shaving and µ2 represent the population mean of swimming times after shaving. Let µd represent the population mean of the differences, X1 - X2. These differences follow a normal distribution. Which of the following would be the most appropriate test and alternative hypothesis to use in testing this theory? A A two-sample t-test with Ha : µ1 > µ2 B A two-sample t-test with Ha : µ1 ≠ µ2 C A two-sample t-test with Ha : µ1 < µ2 D A paired t-test with Ha : µd > 0 E A paired t-test with Ha : µd ≠ 0

D A paired t-test with Ha : µd > 0

A popular computer card game keeps track of the number of games played and the number of games won on that computer. The cards are shuffled before each game, so the outcome of the game is independent from one game to the next and is based on the skill of the player. Let X represent the number of games that have been won out of 100 games. Under which of the following situations would X be a binomial random variable? A All games were played by the same player, whose skill improved over the course of the 100 games B A group of 5 players of different skill levels were each allowed to play 20 games in a row. C A group of players of different skill levels were each allowed to play until they had lost 3 games and this resulted in 100 games played. D Two players of equal skill level each played one game a day for 50 days and their skill level did not change from day to day. E Two players of different skill levels competed by allowing one player to continue until a game was lost, then the other player to continue until a game was lost, and so on, until 100 games were played.

D Two players of equal skill level each played one game a day for 50 days and their skill level did not change from day to day.

A researcher constructed a 95 percent confidence interval for the mean number of alfalfa weevils on an alfalfa plant within a field. Based on 80 randomly selected alfalfa plants, the researcher found an average of 2.5 alfalfa weevils per plant and computed the 95 percent confidence interval to be 1.50 to 3.50. Which of the following statements is a correct interpretation of the 95 percent confidence level? A Approximately 95 percent of alfalfa fields sampled will have an average of 1.50 to 3.50 alfalfa weevils per plant, but nothing can be said about the sample mean number of alfalfa weevils for this or any other field. B Approximately 95 percent of alfalfa fields sampled will have an average of 1.50 to 3.50 alfalfa weevils per plant. The sample mean for this field was 2.50 alfalfa weevils per plant, but the sample means for other fields may be different. C If we repeatedly sampled this field, taking samples of 80 plants and constructing 95% confidence intervals, then, approximately 95 percent of these intervals would include 2.5, the mean for the sample described above. D If we repeatedly sampled this field, taking samples of 80 plants and constructing 95% confidence intervals, then, approximately 95 percent of these intervals would include the population mean number of alfalfa weevils on an alfalfa plant in this field. E If we repeatedly sampled this field, taking samples of 80 plants and constructing 95% confidence intervals, then, approximately 95 percent of these intervals would include the sample mean for that sample.

D If we repeatedly sampled this field, taking samples of 80 plants and constructing 95% confidence intervals, then, approximately 95 percent of these intervals would include the population mean number of alfalfa weevils on an alfalfa plant in this field.

Heights, in inches, for the 200 graduating seniors from Washington High School are summarized in the frequency table below. text... Which of the following statements about the median height is true? A It is greater than or equal to 78 inches. B It is greater than or equal to 72 inches but less than 78 inches. C It is greater than or equal to 66 inches but less than 72 inches. D It is greater than or equal to 60 inches but less than 66 inches. E It is less than 60 inches.

D It is greater than or equal to 60 inches but less than 66 inches.

In a recent poll of 1,500 randomly selected eligible voters, only 525 (35 percent) said that they did not vote in the last election. However, a vote count showed that 80 percent of eligible voters actually did not vote in the last election. Which of the following types of bias is most likely to have occurred in the poll? A Nonresponse bias B Sampling bias C Selection bias D Response bias E Undercoverage bias

D Response bias

A school is having a contest in which students guess the number of candies in a jar. The student whose guess is closest to the correct number of candies in the jar wins a prize. The number of candies guessed by male and female students is shown in the back-to-back stemplot below. text... Which of the following statements is true about the distributions of guesses? A The distribution of guesses for male students is skewed to the left, and the distribution of guesses for female students is skewed to the right. B The distribution of guesses for male students is skewed to the right, and the distribution of guesses for female students is skewed to the left. C The distributions of guesses for male and female students are both skewed to the right. D The distributions of guesses for male and female students are both skewed to the left. E The distributions of guesses for male and female students are both symmetric.

D The distributions of guesses for male and female students are both skewed to the left.

Each person in a random sample of adults was asked how many DVDs he or she owned. Summary statistics are given below. text... Which of the following statements is true? A Seventy-five percent of the adults in the sample own more than 95 DVDs. B Fifty percent of the adults in the sample own between 0 and 129.4 DVDs. C The distribution of the number of DVDs owned appears to be approximately symmetric. D The interquartile range of the number of DVDs owned is 65. E The distribution of the number of DVDs owned contains outliers on both the low side and the high side.

D The interquartile range of the number of DVDs owned is 65.

A controversial issue in the sport of professional soccer is the use of instant replay for making difficult goal line decisions. Each person in a representative sample of 102 players, fans, coaches, and officials was asked his or her opinion about the use of instant replay for goal-line decisions. The data are summarized in the two-way frequency table below. text... In testing to see whether opinion with respect to the use of instant replay is independent of the category of the person interviewed, a chi-square test statistic of 27.99 and a p-value less than 0.001 were calculated. Which of the following statements is correct? A The number of degrees of freedom for the test is 8 - 1 = 7. B The chi-square test should not have been used because two of the counts in the table are less than 5. C The null hypothesis states that there is an association between category and opinion about the use of instant replay, and the small p-value suggests that the null hypothesis should be rejected. D The small p-value suggests that there is evidence of an association between category and opinion about the use of instant replay. E The chi-square test shows that fans favor the use of instant replay.

D The small p-value suggests that there is evidence of an association between category and opinion about the use of instant replay.

Frank, who lives in Texas, and his sister Lilly, who lives in Japan, correspond regularly. From what he can tell from the postmarks on both his and his sister's letters, it appears that it takes longer for Lilly's mail from Japan to reach him in Texas than it does for his letters from Texas to reach her in Japan. When Frank called his post office to ask if there was a reason for this, the postmaster told him that the delivery time of letters in both directions should be the same. Frank and his sister decided to collect data to see if letters from Japan to Texas take longer to be delivered than letters from Texas to Japan. They recorded the delivery time in days. After convincing themselves that the assumptions were reasonable, they performed a two-sample t-test and obtained the following computer output. text... Using a significance level of 0.05, which of the following statements best describes the conclusion that can be drawn from these data? A There is convincing evidence that there is no difference in the mean delivery times. B There is convincing evidence that there is a difference in the mean delivery times. C There is convincing evidence that the mean delivery time from Japan to Texas is greater than the mean delivery time from Texas to Japan. D There is not convincing evidence that the mean delivery time from Japan to Texas is greater than the mean delivery time from Texas to Japan. E The t-test cannot be used for sample sizes that are this small.

D There is not convincing evidence that the mean delivery time from Japan to Texas is greater than the mean delivery time from Texas to Japan.

Each of 133 children in a sample was asked to choose a pencil. Three different colors were available: yellow, red, and blue. The number of 2-year olds and 3-year olds who selected each color is shown in the table above. In a test of independence of age and color, which of the following is used as the expected cell count for 2-year olds who select a yellow pencil?

E

A box contains 10 tags, numbered 1 through 10, with a different number on each tag. A second box contains 8 tags, numbered 20 through 27, with a different number on each tag. One tag is drawn at random from each box. What is the expected value of the sum of the numbers on the two selected tags? A 13.5 B 14.5 C 15.0 D 27.0 E 29.0

E 29.0

Each value in a sample has been transformed by multiplying by 3 and then adding 10. If the original sample had a variance of 4, what is the variance of the transformed sample? A 4 B 12 C 16 D 22 E 36

E 36

A pollster is interested in comparing the proportions of women and men in a particular town who are in favor of a ban on fireworks within town borders. The pollster plans to test the hypothesis that the proportion of women in favor of the ban is different from the proportion of men in favor of the ban. There are 4,673 women and 4,502 men who live in the town. From a simple random sample of 40 women in the town, the pollster finds that 38 favor the ban. From an independent simple random sample of 50 men in the town, the pollster finds that 27 favor the ban. Which of the following statements is true about this situation? A Because the samples are from normal populations, a two-proportion z-test would be valid. B Because the size of each sample is greater than 30, a two-proportion z-test would be valid. C Because the number who favored the ban is greater than 10 in both groups, a two-proportion z-test would be valid. D Because of the relative sizes of the populations and samples, a two-proportion z-test would be valid. E A two-proportion z-test would not be valid for these data.

E A two-proportion z-test would not be valid for these data.

A department store manager wants to know if a greater proportion of customers on the store's mailing list would redeem a coupon for $5 off the price of an item than would redeem a coupon for 10 percent off the price of anitem. The manager mails a $5 off coupon to a random sample of 500 customers and mails a 10 percent off coupon to an independent random sample of 500 customers. The number of coupons of each type that were redeemed was recorded. Assuming that the conditions for inference are met, what test procedure should be used to answer the manager's question? A A one-sample t-test for a mean B A one-sample z-test for a proportion C A t-test for the slope of a regression line D A matched-pairs t-test for a mean difference E A two-sample z-test for a difference between two proportions

E A two-sample z-test for a difference between two proportions

Professor James gave the same test to his three sections of statistics students. On the 35-question test, the highest score was 32 and the lowest was 15. Based on the information displayed in the boxplots above, which of the following statements is true? A Section 1 has the smallest interquartile range. B The lowest score in section 2 is higher than the highest score in either of the other sections. C Section 2 has the smallest range of scores. D The top 25% of scores in section 2 are lower than the highest score in section 3. E At least 50% of the scores in section 3 are higher than all of the scores in section 1.

E At least 50% of the scores in section 3 are higher than all of the scores in section 1.

A well-designed experiment should have which of the following characteristics? I. Subjects assigned randomly to treatments II. A control group or at least two treatment groups III. Replication A I only B I and II only C I and III only D II and III only E I, II and III

E I, II and III

A newspaper poll found that 52 percent of the respondents in a large random sample of likely voters in a district intend to vote for candidate Smith rather than the opponent. A 95 percent confidence interval for the population proportion was computed to be 0.52 ± 0.04. Based on the confidence interval, which of the following should the newspaper report to its readers? A Smith will win because a majority of voters are in favor of Smith. B There is a 95% chance that Smith will win. C The poll predicts Smith will win, but there is a 5% chance that the prediction is incorrect due to sampling error. D With 95% confidence, there is convincing evidence that Smith will win. E No prediction about who will win can be made with 95% confidence.

E No prediction about who will win can be made with 95% confidence.

A one-sided hypothesis test is to be performed with a significance level of 0.05. Suppose that the null hypothesis is false. If a significance level of 0.01 were to be used instead of a significance level of 0.05, which of the following would be true? A Neither the probability of a Type II error nor the power of the test would change. B Both the probability of a Type II error and the power of the test would decrease. C Both the probability of a Type II error and the power of the test would increase. D The probability of a Type II error would decrease and the power of the test would increase. E The probability of a Type II error would increase and the power of the test would decrease.

E The probability of a Type II error would increase and the power of the test would decrease.

Which of the following statements must be true about the data sets A and B displayed in the histograms above? A The mean of data set A is equal to the mean of data set B. B The median of data set A is equal to the median of data set B. C The range of data set A is equal to the range of data set B. D The standard deviation of data set A is less than the standard deviation of data set B. E The standard deviation of data set A is greater than the standard deviation of data set B.

E The standard deviation of data set A is greater than the standard deviation of data set B.