I need help on how to average more than 30 numbers in more than 30
worksheets.

If you mean numbers in the same position on different worksheets, try:
=AVERAGE(Sheet1:Sheet31!E3)

If the cells differ from sheet to sheet, you have to enter each
individually:
=Sheet1!A1 + Sheet2!B2 + Sheet3!C3 + ... + Sheet31!AE31

Excel 2007 allows up to 255 values in AVERAGE and other functions.


Niek Otten wrote:

And if you just put an extra pair of brackets around the list of cells, it
is considered one argument. I do not know how many cells you can put in a
list like this, but certainly more than 30...

I think you can include up to 32,768 areas in function arguments, so the
formula length limitation always comes first. This has been extended in
Excel 2010.

You can test this by entering =sum((s,s,s,s)) where s:=selection() is a
defined name. First select 8192 values in alternate rows using gotospecial
(the maximum allowed up to Excel 2007), press Ctrl+Alt+F9 to recalculate.
Now try replacing the formula with =sum((s,s,s,s,a1)), select rows and
recalculate and it runs out of memory. (Ignore circular references and make
sure to save first!)