The method of tree-ring dating gave the following years A.D. for an archaeological excavation site. Assume that the population of x values has an approximately normal distribution. 1,320 1,201 1,215 1,320 1,268 1,316 1,275 1,317 1,275 LO USE SALT (a) 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 = A.D. S = yr (b) When finding an 90% confidence interval, what is the critical value for confidence level? (Give your answer to three decimal places.) to = What is the maximal margin of error when finding a 90% confidence interval for the mean of all tree-ring dates from this archaeological site? (Round your answer to the nearest whole number.) E = Find a 90% confidence interval for the mean of all tree-ring dates from this archaeological site. (Round your answers to the nearest whole number.) lower limit A.D. upper limit A. D