Assume that a sample is used to estimate a population mean μ. Find the 99.9% confidence interval for a sample of size 70 with a mean of 67.8 and a standard deviation of 6.2. Enter your answer as an open-interval (i.e., parentheses) accurate to one decimal place (because the sample statistics are reported accurate to one decimal place).
99.9% C.I. = (65.4,70.2)
Answer should be obtained without any preliminary rounding. However, the critical value may be rounded to 3 decimal places.