Assume that a sample is used to estimate a population mean . Find the 80% confidence interval for a sample of size 47 with a mean of 57.5 and a standard deviation of 18.9. 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). 80% C.I. = Answer should be obtained without any preliminary rounding. However, the critical value may be rounded to 3 decimal places.