08 STAT HWA q estimation

# 08 STAT HWA q estimation - Professor Valerie R Bencivenga...

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Professor Valerie R. Bencivenga Economics 329 PRACTICE ASSIGNMENT #8A: ESTIMATION 1. An economist wants to estimate the mean number of days lost to absenteeism per year among professional employees in the financial services industry. Based on past research, the distribution of annual days of absenteeism among such employees is approximately normal with standard deviation 5 days. a. A random sample of 10 employees yields a sample mean of 6.3 days. Give the 95% confidence interval for the population mean. b. How many employees should be sampled in order for a 95% confidence interval to have a margin of error of no more than 0.1 day? (This means the length of the confidence interval is no more than 0.2 days.) 2. A consultant for the World Bank wants to estimate the mean and variance of interest rates charged by landlords on loans made to their tenant farmers in Bihar, India. She takes a random sample of 36 loans. A normal plot of these data shows it is reasonable to assume an approximately normal distribution for these interest rates. The sample mean interest rate is 85 percentage points, and the sample standard deviation of interest rates is 21 percentage points. a. Give the 99% confidence interval for the population mean interest rate. b. Give the 99% confidence interval for the population variance of interest rates. 3. a. A few years ago, the Austin American-Statesman reported the results of a survey of costs of banking. One question concerned annual fees paid to maintain a checking account. In a random sample of 34 banks surveyed in Texas, average fees were \$197.70. Assume that fees are approximately normally distributed. Let’s suppose that the sample standard deviation of fees was \$60. Give the 95% confidence interval for the population mean level of fees. b.

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08 STAT HWA q estimation - Professor Valerie R Bencivenga...

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