We use thet distribution to construct a confidence interval for the population mean when the underlying population standard deviation is not known. Under the assumption that the population is normally...

Extracted text: We use thet distribution to construct a confidence interval for the population mean when the underlying population standard deviation is not known. Under the assumption that the population is normally distributed, find ta/2, df for the following scenarios. (You may find it useful to reference the t table. Round your answers to 3 decimal places.) a. A 90% confidence level and a sample of 25 observations. b. A 95% confidence level and a sample of 25 observations. A 90% confidence level and a sample of 19 observations. A 95% confidence level and a sample of 19 observations. C. d.