Sum dynamic number of worksheets into one

[SherryO]

I have several workbooks with multiple worksheets, the number of which changes everyweek. I would like to have a summation worksheet that totals the data of the individual worksheets built on the fly, but I don't know how to go about it. Any help would be appreciated. Thanks

[Bob Phillips]

Create a sheet called First, put that at the start, another called Last, out that at the end, then use

=SUM(First:Last!A10)

for example

[SherryO]

THANK YOU!