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4. [-/0.3 Points] DETAILS BBUNDERSTAT12 7.2.013.FB.S. MY NOTES ASK YOUR TEACHER PRACTICE ANOTHER 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. 1,229 1,306 1,320 1,236 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 x and sample standard deviation s. (Round your answers to four decimal places.) X = A.D. S 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 A.D. upper limit A.D