The standard deviation is the square root of the variance and is equal to 4.907477The correct answer is: 4.907477Information Not flaggedFlag questionInformation textLet X be amount of time (in minutes) a postal clerk spends with his/her customer.Assume that X has an Exponential(?) distribution and that E(X) = 7 minutes. Thenext 3 questions refer to this waiting time. (The answer may be rounded up to 3decimal places of the actual value.)Question 20IncorrectMark 0.00 out of 1.00 Not flaggedFlag questionQuestion textThe rate ? is equal toAnswer:0

IncorrectFeedbackThe expectation in the Exponential distribution is the reciprocal of theparameter ?.Consequently, the parameter ? is equal to the inverse of theexpectation: ? = 1/E(X). The expectation E(X) = 7, hence ? = 1/7 = 0.1428571The correct answer is: 0.1428571Question 21IncorrectMark 0.00 out of 1.00 Not flaggedFlag questionQuestion textThe probability that a clerk spends between four to five minutes with a randomlyselected customer isAnswer:0IncorrectFeedbackLet the distribution of X be Exponential(1/7). The probability P(4 = X = 5) isequal to the difference between P(X = 5) and the probability P(X < 4). The letterprobability is equal to P(X = 4), since the distribution is continuous. Thisdifference can be computed with the code: > pexp(5,1/7)-pexp(4,1/7) [1] 0.07517646The correct answer is: 0.07517646Question 22IncorrectMark 0.00 out of 1.00 Not flaggedFlag questionQuestion textThe probability that a clerk spends more than 10 minutes with a customer isAnswer:0IncorrectFeedbackLet the distribution of X be Exponential(1/7). The probability P(10 < X) is equalto the difference between 1 and the probability P(X = 10). This difference can becomputed with the code: > 1-pexp(10,1/7) [1] 0.2396510The correct answer is: 0.239651------------------------------------------------------------------------Information Not flaggedFlag questionInformation textApproximately 85% of statistics students do their homework in time for it to becollected and graded. Let X be the number students that submit their homework intime out of a statistics class of 70 students. The following 4 questions refer tothis X. (The answer may be rounded up to 3 decimal places of the actual value.)Question 1CorrectMark 1.00 out of 1.00 Not flaggedFlag questionQuestion textThe sample space of X is:Select one:a. The numbers between 0 and 1.b. The integers between (and including) 0 and 70. Correctc. The collection {0, 1,...,85}d. The collection {"Submit on time", "Do not submit on time"}.FeedbackThe possible outcome of X, the number of students out of 70 that submit theirhomework, is an integer and the range of values starts at 0 (no one submits) andends in 70 (all submit).The correct answer is: The integers between (and including) 0 and 70.Question 2CorrectMark 1.00 out of 1.00 Not flaggedFlag questionQuestion textThe probability that less than 60 of the 70 students will do their homework on timeis:Answer:0.4842268

CorrectFeedbackLess that 60 means 59 or less. The probability P(X = 59) can be computed with thecode: > pbinom(59,70,0.85) [1] 0.4842268The correct answer is: 0.4842268Question 3CorrectMark 1.00 out of 1.00 Not flaggedFlag questionQuestion textThe expectation of X is:Answer:59.5CorrectFeedback

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