Auto Updating Column Sum

I would like to know if anyone is able to tell me if it is possible to do a sum as follows;

divide the total value of a column by the number of entries in that column.

IE; I run a spreadsheet which is update d at least once a day.  I would like to have an analysis on a seperate worksheet (or even another page to the side of the original worksheet) whereby a formual will add the total figures in say column B, recognise the number of entires (say 17 entries in the same column over 42 rows) and divide the total of that column by 17.  I also need it recalculate as I add more figures to that column.

I guess what I am looking for is an ongoing, updated average of the total figures in column B (for instance)

I hope I have made this clear - thanks for the help.