Calculating blank cells, IF & SUM

Morning,

For years I've found answers on this forum without ever needing to join and open a thread. However the day has finally come.

Aim of the spreadsheet:
My colleagues at work designed a simple spreadsheet to monitor participation rates for various sports events at 3 different locations. I'm trying to make it summarise these numbers over the course of 7 weeks. There are 2 summary sheets, one that summarises both male and female participation together and one that summarises only female participation, for each location. After week 2 on the summary sheet there are columns to calculate percentage rise or fall. I've attached the document, feel free to take a look.

The problem:
I don't want excel to calculate percentage fall between weeks before both weeks figures have been inputted. In the Female Summary section I've managed to achieve this with this formula: =IF('Week 2'!D41="","",'Week 2'!D41)

However in the General formula I can't work it out. It's quite hard to explain so feel free to take a look and I will answer any questions.

I'd have thought this would work: =IF('Week 2'!C41:D41="0","",'Week 2'!C41:D41)
It doesn't though for some reason.


Cheers

Ollie

Like this?

=IF(SUM('Week 1'!C41:D41)=0,"",SUM('Week 1'!C41:D41))

btw on summary general cell I3 you must change a little like this:

=IF(OR(B3="",F3=""),"",SUM((F3-B3)/B3))

Try this:

=IF(SUM('Week 1'!C41:D41)=0,"",SUM('Week 1'!C41:D41))

but it looks like your data would benefoiit from a bit more organisation, the the formula can't be copied down, since your entries in Col A don't fall in a numerical sequence