The method of tree ring dating gave the following years A.D. for an archaeological excavation site. Assume that the population ofxvalues has an approximately normal distribution.1306 1278 1236 1320 1268 1316 1275 1317 1275

Use a calculator with mean and standard deviation keys to find the sample mean yearxand sample standard deviations. (Round your answers to the nearest whole number.)

x=A.D.

s=yr

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 limitA.D.

upper limitA.D.