Let's consider the annual precipitation levels in Los Angeles county. Suppose the average annual precipitation in LA county is normally distributed with a mean of 15 inches and a standard deviation of 3 inches. We can classify the precipitation levels in the following way: Dry Annual precipitation is more than 1 standard deviation below the mean. Normal  Annual precipitation is less than 1 standard deviations below the mean and less than 2 standard deviation above the mean. Humid  Annual precipitation is more than 2 standard deviations above the mean. Before answering the following questions it may be helpful to mark on a bell shaped curve where the above regions lie.  According to the empirical rule, what is the probability of experiencing a Dry year in Los Angeles? According to the empirical rule, what is the probability of experiencing a Humid year in Los Angeles?     According to the empirical rule, what is the probability of experiencing a Normal year in Los Angeles?

Definition Definition Measure of central tendency that is the average of a given data set. The mean value is evaluated as the quotient of the sum of all observations by the sample size. The mean, in contrast to a median, is affected by extreme values. Very large or very small values can distract the mean from the center of the data. Arithmetic mean: The most common type of mean is the arithmetic mean. It is evaluated using the formula: μ = 1 N ∑ i = 1 N x i Other types of means are the geometric mean, logarithmic mean, and harmonic mean. Geometric mean: The nth root of the product of n observations from a data set is defined as the geometric mean of the set: G = x 1 x 2 ... x n n Logarithmic mean: The difference of the natural logarithms of the two numbers, divided by the difference between the numbers is the logarithmic mean of the two numbers. The logarithmic mean is used particularly in heat transfer and mass transfer. ln x 2 − ln x 1 x 2 − x 1 Harmonic mean: The inverse of the arithmetic mean of the inverses of all the numbers in a data set is the harmonic mean of the data. 1 1 x 1 + 1 x 2 + ...