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BT Thirdexam version3 - Problem Points 1 2 3 4 5 6 7 8 12...

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Problem Points Earned 1 12 2 12 3 12 4 12 5 12 6 12 7 13 8 15 Total 100 0 1). (12 pts) A company is satisfied with the performance of the Accounts Receivable division of their company, if bills to customers are paid within 4 calendar weeks of the date of mailing. In order to measure perfomance, a random sample of 15 bills is sampled from a large number of customer billings. The time till the receipt of payment is shown below. Determine if this data indicates whether or not the Accounts Receivble division is Days till Bill was paid. 26 26 28 24 23 27 29 30 29 33 31 26 25 30 28 mean = 27.67 stdev = 2.74 Using the template from file "onesam.xls": Template for Confidence Interval Sample Sample Sample Mean SD n alpha Enter ===> 27.67 2.74 15 0.05 Confidence Interval is 26.15 to 29.19 Since 28 days is included in the confidence interval, we accept the Null Hypothesis (i.e. functioning satisfactorily. (Use α = .05).
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. the department is functioning satisfactorily).
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2. (12 pts) An auditor would like to determine the average cost per day of business trips taken by company employees to within five dollars. Based on past data, the standard deviation of the average cost per day on business trips is approximately thirty dollars. How large a We know that n >= (t^2 * s^2) / (W^2), where t can be approximated by z (normal distrib s 30 W 5 alpha 0.05 z 1.96 n >= 138.29 The sample must therefore be at least size 139 in order to determine the cost within $5 Basic Sam Enter Stan Enter desid for confide Enter desir Required S Enter Popu Required S Finite Popu sample must she take if is she uses α = .05 ?
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bution) for a sample size greater than 30, s is 30, and W is 5. 5 with a 95% confidence. mple Size Computation For the Mean from a Single Sample ndard Deviation =====> 30 dered +/- figure ence interval =====> 5 red confidence Level =====> 0.95 Sample Size n = 139 ulation Size =====> 0 Sample Size for a ulation n = 139
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3. (12 pts) An automobile dealership knows from experience that most people will want to test drive a car before buying it. Accordingly their goal is get half of the serious sales prospects to test drive a vehicle when they visit the dealership. Last month of one hundred serious prospects, thirty five test drove a vehicle during their visit to the dealership. Is the dealership Expected Observed Test drove 50 35 -15 4.5 Not Drove 50 65 15 4.5 Total serious prospec 100 100 9 Chi-square contributions: 0 Test drove 4.5 Not Drove 4.5 Total Chi-square: 9 One-sided p-value (1 df): 0 Using alpha = 0.01, we would reject the Null Hypothesis, and therefore conclude that w What would be an acceptable range ? chiinv(0.01,1) = 6.63 Noting that the problem is symmetric, each contribution should be no more than: Therefore the observed values should be + or - 12.88 around 50.
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