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. 1,222 1,271 1,208 1,257 1,268 1,316 1,275 1,317 1,275 la USE SALT (a) Use a calculator with mean and standard deviation keys to find the sample mean year; and sample standard deviation 5. (Round your answers to four decimal places.) 7:: 1269.222 3.; AD. 5 = 33.8223 X yr (b) 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 1248.2522 X A.D. upper limit 1290.192 I A.D