At Burnt Mesa Pueblo, archaeological studies have used the method of tree-ring dating in an effort to determine when prehistoric people lived in the pueblo. Wood from several excavations gave a mean of (year) 1257 with a standard deviation of 31 years. The distribution of dates was more or less mound-shaped and symmetric about the mean. Use the empirical rule to estimate the following.

(a) a range of years centered about the mean in which about 68% of the data (tree-ring dates) will be found between and A.D. (b) a range of years centered about the mean in which about 95% of the data (tree-ring dates) will be found between and A.D. (c) a range of years centered about the mean in which almost all the data (tree-ring dates) will be found between and A.D.