See exemple:

http://cjoint.com/?bofTWZd7rT

Case 1: NamesSheets contains names of sheets to add:

=SUMPRODUCT(SUMIF(INDIRECT(NamesSheets&"!B2"),"Yes ",INDIRECT
(NamesSheets&"!A2")))

Case 2: Generic names Feuil1,Feuil2,....

=SUMPRODUCT(SUMIF(INDIRECT("Feuil"&ROW(INDIRECT("1 :4"))&"!B2"),"Yes",
INDIRECT("Feuil"&ROW(INDIRECT("1:4"))&"!A2")))

JB
http://boisgontierjacques.free.fr

On 13 jan, 22:11, JeffPlax wrote:
I have a series of spreadsheets, and I need to sum the hours only if they are
billable

column A contains hours, and column B indicates weather hours in column A
are billable or not (Yes or No). *Does SUMIF work using 3D-references?