Question : Multiple Conditional Formatting cell problem

I'm trying to create a spreadsheet for our traffic office, and I need to keep a check on what trailers we are using.  To this end, I have list of trailers in one section of the spreadsheet.  If a trailer is used, it gets entered into a different cell.  Then when the job is finished, another cell is marked to show the job is finished and the trailer is back in our yard and available for use.

If a trailer is used, I have the conditional formatting set to change the list entry to white text so it 'disappears' from the sheet and we know it has been used.  However, what I want to do is to have the formatting change if the 'finished' cell is marked.

The first part I have done easily by using the formula '=COUNTIF($C$5:$C$13,E5)', where C5:C13 are where I enter the trailer number, and E5 is the first cell containing my list of trailers.  

What I am stuck on is changing the colour back if the 'finished' cell is marked.  I have tried using a COUNTA formula to see if the cell is blank, but don't know how to relate this to the trailer used.

I've attached a sample of what I have so far.  As you can see, I have used trailer 7 and marked it as returned, but it is the trailer next to the cell that has changed.  How can I make it trailer 7 that shows in red?

Thanks in advance!

Attachments:

Trailertest.xls (21 KB) (File Type Details) 

Trailer conditional formatting test

Answer : Multiple Conditional Formatting cell problem

Try using this one formula:

=SUMPRODUCT(($C$5:$C$13=E5)*($D$5:$D$13<>"a"))>0

See attached file.