The total value at the bottom of a column is the total of all values above it in the report. The same is true of the average value at the bottom of a report. The average value is the average of all the values in the column above it. The totals and averages at the bottom of a formula field do not necessarily relate to the totals and averages of fields that make up the formula in the way that the formula specifies. For example imagine ten rows and three fields. All cells have the value one in them. Totals are turned on for all three columns. Imagine that the third column is a formula field that divides the first column by the second column. The totals at the bottom of all three columns will display "10". However if you divide the total of column one by the total of column two you get the number one not the number 10! However in this case the average at the bottom of each column is one, which does follow the formula, but this is only a coincidence.

Here's another example:

10 5 2
100 1 100
------------
110 6 102 Totals
55 3 51 Averages

In the above example the third column is a formula numeric field that divides the first column by the second column. Notice that in the Totals and Averages rows they represent the totals and averages of the numbers in the column above. However in the Totals row if you divide 110 by 6 you don't get 102 or even 51! And if you divide 55 by 3 in the Averages row you don't get 51 or even 102.