(b) Find a 90% confidence interval for the mean of all tree-ring dates from this archaeological site. To find a confidence interval for the mean of all tree-ring dates from this archaeological site, you will need a point estimate for /, and you will either need to know the population standard deviation or estimate it in order to calculate the margin of error. In the previous step you calculated the sample mean, x = 1,278.5556. Use this as your point estimate for u. You also calculated the sample standard deviation, s = 34.5475. To compute a confidence interval for u, you will need a critical value from Student's t distribution with n - 1 degrees of freedom. This number, to, is the number such that an area equal to c under the t curve falls between -to and t . Use the table to find the critical value for a confidence level of 90%. We found earlier that n = 9, thus the degrees of freedom are n - 1 = Use the table to find to . to.90 = Submit Skip (you cannot come back)