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) 1245 with a standard deviation of 32 years. The distribution of dates was more or less moundshaped and symmetrical 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.
A person's blood glucose level and diabetes are closely related. Let x be a random variable measured in
milligrams of glucose per deciliter (1/10 of a liter) of blood. Suppose that after a 12-hour fast, the
random variable x will have a distribution that is approximately normal with mean ? = 88 and standard
deviation ? = 21. Note: After 50 years of age, both the mean and standard deviation tend to increase.
For an adult (under 50) after a 12-hour fast, find the following probabilities. (Round your answers to
four decimal places.)
(a) x is more than 60
(b) x is less than 110
(c) x is between 60 and 110
(d) x is greater than 140 (borderline diabetes starts at 140)