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 1,264 1,215 1,271 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 year x and sample standard deviation s. (Round your answers to four decimal places.)


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.)
tc =
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.