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.

1278 | 1306 | 1215 | 1222 | 1268 | 1316 | 1275 | 1317 | 1275

(a) 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.)

• xbar=_______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.