A sample of 17 observations is selected from a normal population where the population standard deviation is 16. The sample mean is 53.
a. Determine the standard error of the mean. (Round the final answer to 3 decimal places.) The standard error of the mean is .
b. Determine the 80% confidence interval for the population mean. (Round the z-value to 2 decimal places. Round the final answers to 3 decimal places.) The 80% confidence interval for the population mean is between and .
c. If you wanted a wider interval, would you increase or decrease the confidence level?