A sample of 25 observations is selected from a normal population where the population standard deviation is 32. The sample mean is 77. a. Determine the standard error of the mean. (Round the final answer to 3 decimal places.) The standard error of the mean is 6.400 . b. Determine the 95% confidence interval for the population mean. (Round the z-value to 2 decimal places. Round the final answers to 3 decimal places.) The 95% confidence interval for the population mean is between 63.790 and 90.210 . c. If you wanted a wider interval, would you increase or decrease the confidence level?