Use a calculator with mean and standard deviation keys to find the sample mean year x and sample standard deviation s. (Round your answers to four decimal places.) x = 1289.4444 Correct: Your answer is correct. A.D. s = 19.9318 Correct: Your answer is correct. yr (b) When finding an 90% confidence interval, what is the critical value for confidence level? (Give your answer to three decimal places.) tc