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.

1,264

1,292

1,320

1,257

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.)

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.)

t_c =

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.