Is it possible to run a simple SUM, AVERAGE formulas over worksheets that havent been created yet.

I have a fixed template which records data from different days, each day has a separate worksheet. I also have a summary sheet which totals, averages figures over those days. Instead of altering the summary sheet everytime i add a sheet for a particular day is it possible to create a forumula which can capture data from any further worksheets that are created.

Thanks

Mark