Chapter 8 Practice Problems

# Chapter 8 Practice Problems - Lafayette residents within a...

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Chapter 8: Practice Problems Q1. The average monthly electric bill of a random sample of 64 residents of Lafayette is \$80 with a standard deviation of \$24. a. Construct a 95% confidence interval for the population mean of monthly electric bills of Lafayette residents. b. Construct a 99% confidence interval for the population mean. c. What effect do you observe as the confidence level is increased? d. What happens to the 95 % confidence interval for the population mean if the sample size was 100 with the same sample mean and same sample standard deviation as above?

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e. What effect will you observe to the 95 % confidence interval for the population mean if the sample standard deviation were \$30 instead of \$24? f. Assume that a sample mean of \$75 and a sample standard deviation of \$22 were obtained for a random sample of 25 residents of Lafayette. Construct a 95% confidence interval for the population mean of monthly electric bills. What assumption did you make? g. If we want to estimate the population mean of monthly electric bills of

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Unformatted text preview: Lafayette residents within a margin of error of \$2 with 95% confidence, what sample size should we use? Assume a population standard deviation of \$20. h. If the desired margin of error is fixed at \$2, what happens to the sample size as the confidence level is increased to 99% in part (g)? Q2. An American Express retail survey found that 180 out of a total of 1200 U.S. consumers had used the Internet to buy gifts during the 1999 holiday season. a. What is the point estimate of the population proportion of consumers using the Internet to buy gifts? b. Using 95% confidence, what is the margin of error associated with the estimated proportion? c. Construct the 95% confidence interval estimate of the population proportion of customers using the Internet to buy gifts. d. How large a sample should be taken if the desired margin of error is 3%? Use 95% confidence and p = 0.16....
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## This note was uploaded on 12/06/2011 for the course MGMT 305 taught by Professor Priya during the Fall '08 term at Purdue University-West Lafayette.

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Chapter 8 Practice Problems - Lafayette residents within a...

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