 The Statistic Meaning Center

 Number, n, is the statistic describing how big the set of numbers is, how
many pieces of data are in the set.

Average is the statistic
which describes the center of a set of data, a set of numbers which are measurements or counts.
 The most commonly used averages are the
mean (arithmetic average),
mode (most frequent number),
median (middle number when numbers are listed smallest to largest).
 [Please visit each link in the above paragraph to see how each statistic is
computed.]
 Each average, you see, has a different meaning 
describes a different center.
 The mean, for example, is the average computed by adding each piece of
data, each number in the set, then dividing the total by n, the number of numbers. See
mean.
 For a sample of numbers, add the numbers,
divide by the number of numbers, n.

 For the entire set (a population) of numbers,
add the numbers, divide by the number of numbers, n.
