Margin of error = 1.645 * 10.5/ sqr 120 = 1.5768 c. Construct a 95% confidence interval for the mean unit cost of the population if the sample unit cost is obtained from a random sample of 150 instead of 100. Given u=$25 o=$10.5 n = 200 95% confidence interval for the mean unit cost of the population is Mean = $25 + - 1.96 * 10.5/ sqr 200 =23.545, 26.445 d. Based on the results from a. and c., what can you say about the effect of a larger sample size on the length of the confidence interval at the same confidence level? By increasing the sample size, the length of the confidence interval will decrease 5. A simple random sample of 60 items is taken from an inventory and the average unit cost on the items is $23.5. The population standard deviation is unknown. Instead the sample standard σ deviation s is also calculated from the sample and is found to be $12.2. ( 4 points ) a. Construct a 99% confidence interval for the mean unit cost of the population. 19.309,27.691 b. What is the margin of error at the 95% confidence level? 3.154 6. The average score on an employee satisfaction survey is found to be 3.75 (out of 5). The sample standard deviation is 1.24. These two statistics are calculated from a random sample of 25 employees in a mid-size professional firm. ( 4 points ) a. With 95% confidence, what is the margin of error? 0.5116
b. What is the 95% confidence interval estimate of the population mean score? (4.216,3.23) 7. Annual starting salary for graduates of the BBA program in a Canadian University is expected to be between $35,000 and $55,000. A survey involving a random sample of graduates from this program is planned and the first order of business is to decide on an appropriate sample size. As usual, the 95% level of confidence will be used. ( 6 points ) a.
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- Winter '15