An average gives us information about some class of things, S;
what it tells us is the central value of Ss on some quantitative
There are two different kinds of average: the arithmetic mean
and the median.
To find the arithmetic mean, you add up the values of each S and
then divide by the number of Ss.
The median score is the one that lies in the middle of all the
scores, so that an equal number of scores are higher and lower.