Statistics 211 Practice Exam 2 Answer key

1 Statistics 211 Practice Exam 2 Answer key1. The formula E(X) = np can be used to find the expected value of a. any numeric random variableb. only Poisson random variablesc. only normal random variablesd. only binomial random variables *e. none of the above2. For a specific sample size, the width of a 95% confidence interval on a. would be larger than the width of a 90% confidence interval on . *b. would be smaller than the width of a 90% confidence interval on .c. would be the same as the width of a 90% confidence interval on .d. cannot be compared to the width of a 90% confidence interval on .e. none of the above3. A random sample of 400 WVU students was selected, in which 150 students stated thatthey had used an illegal drug.

2 A 95 % confidence interval on binomial parameter pgoes from to Which of the following statements provides the appropriateinterpretation of this 95 % confidence interval?a. 95% of all WVU students use an illegal drug between and of There is a 95% probability that a randomly selected WVU student has used anillegal We are 95% confident that between and of all WVU studentshave used an illegal drug. *d. We are 95% confident that between and of the sample of 400 WVU students have used an illegal none of the above4. The standard normal distribution is a normal distribution whosea. mean is =1 and standard deviation =0b. mean is =0 and standard deviation =1 *c. mean can have any real value and standard deviation =1d. mean can be determined by using a z-scoree.

3 None of the above5. A radar gun is used to measure the speed of 74 randomly selected automobiles onInterstate 79, and the data is used to construct a 95% confidence interval on the meanspeed of all automobiles on I-79. The 95 % confidence interval goes from mph mph. Which of the following statements provides the appropriate interpretation ofthis 95 % confidence interval?a. 95% of all automobiles on I-79 travel between mph and There is a 95% probability that the mean speed of all automobiles on I-79 isbetween mph and We are 95% confident that the mean speed of all automobiles on I-79 isbetween mph and mph. *d. There is a 5% probability that the mean speed of all automobiles on I-79 isbetween mph and none of the above6.

4 Scores on the math section of a college entrance exam are normally distributed withmean = and standard deviation = Find the probability that a randomly selectedtest-taker will score 25 or higher on the math section of this *c. none of the above7. Every normal distributiona. is symmetric about its mean =0b. is symmetric about its mean , but the mean is not necessarily 0 *c. is asymmetricd. parts b) and c) onlye. none of the above8. On a multiple-choice exam, there are 5 possible answers to each of 20 questions. Eachquestion has only one correct Answer . A student, J , has not studied and must guess theanswer to each question (you may assume that the guesses are independent of eachother). The mean number of correct guesses that J can expect to obtain isa.

5 5b. 10c. 4 *d. 2e. none of the above9. A random sample of 400 WVU Stat211 students was selected, in which 72 studentsstated that they did not attend their Statistics lab session last week. A 99% confidenceinterval on p, the probability that a randomly selected WVU Stat211 student did notattend his/her Statistics lab session last weeka. has lower limit and upper limit has lower limit and upper limit has lower limit and upper limit *d. cannot be computed using the information providede. is none of the above10. Twenty-three percent of college freshmen do not return to college for theirsophomore year of study. A random sample of 12 college freshmen is obtained. Theprobability that exactly four of the 12 freshmen will not return for their sophomore yearisa.

6 *b. none of the above11. A random sample consisting of 64 observations is collected from a population withmean 75 and standard deviation 32. The probability that the sample mean will have valuethat is less than 83 isa. not computable given the information providedb. *e. none of the above12. Before we use the Poisson distribution to approximate a binomial probability, wemusta. make sure that the original experiment is a binomial experimentb. check that the (three) conditions for using the Poisson approximation aresatisfiedc. set =npd. all of the above *e. parts b) and c) only13. Vendco Company owns a soda pop vending machine in the lobby of their officebuilding. For a random sample of 14 days during the year 2004, data was collected on thenumber of cans of soda pop sold each day.

7 The sample mean was cans with a sampledeviation of cans. Construct a 95% confidence interval on the mean number of cansold per day during The 95 % confidence interval goes from to cans per The 95 % confidence interval goes from to cans per day. *c. The 95 % confidence interval goes from to cans per The 95 % confidence interval cannot be calculated because the sample size isless than 30 observations. e. The 95 % confidence interval goes from to cans per Assume that the amount of time PRT riders spend waiting for a PRT car is normallydistributed with a mean = minutes and standard deviation = minutes. Find theprobability that a randomly selected PRT rider must wait less than 18 minutes for thenext PRT *d.

8 None of the above15. An individual measurement, , a data value, consists of which three components:a. the sample, the observational unit, and the researcherb. the true value, the bias, and chance (or random) error *c. the population, the sample, and the sample meand. the population mean, the sample mean, and the sample standard deviatione. none of the above16. A random sample of 10 observations is selected from a normal distribution withpopulation mean equal to 75 and a population standard deviation equal to 20. The meanof x-bar s distribution ( , the sampling distribution of the sample mean)a. cannot be determined from the information providedb. will be equal to 75 *c. will be equal to 20d. will be equal to none of the above17. Dr.

9 Digme, an archaeologist, estimates that, on the average, she recovers onesignificant historical artifact per fifty cubic yards of dirt that she excavates. During thesummer of 2007 Dr. Digme plans to excavate 100 cubic yards of dirt. The probability thatDr. Digme will recover at least 3 significant historical artifacts isa. *c. none of the above18. Hot Head Hat Company specializes in custom printing on hats. Hot Head HatCompany averages two custom orders per week. The probability that this companyreceives exactly 3 custom hat orders next week isa. *b. none of the above19. On a multiple-choice exam, there are 5 possible answers to each of 20 question has only one correct Answer . A student, J , has not studied and mustguess the Answer to each question (you may assume that the guesses are independent ofeach other).

10 J must Answer at least 10 questions correctly in order to pass the probability that J will pass the exam isa. *d. none of the above20. The probability distribution for a single toss of a fair tetrahedral (four-sided) die isX | 1 2 3__ 4____P(X) | expected value of X is a. 1b. 2c. 3d. 4e. none of the above *21. A sample surveya. attempts to acquire data from every member of a populationb. attempts to acquire data from a subset of a population *c. is the same as a sampling framed. is the same as a censuse. none of the above22. A simple random samplea. is obtained in such a way as to ensure that every member of the population hasan equal chance of being selectedb.