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.

1,187

1,180

1,285

1,236

1,268

1,316

1,275

1,317

1,275

(a)Use a calculator with mean and standard deviation keys to find the sample mean yearxand sample standard deviations. (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.