TTEST with gaps in data

[hhd]

Hi there,
I've been trying all last week but to no avail.
I have a set of data (grades) that have been filtered using if statement (for teachers).
Now I 2 seperate sets of data.
The columns have blanks, no grades (no grades but =IF(C4=TRUE, A4,"")
When I use a ttest I want it to ignore the "false" data
example.jpg

edit:
here is the file
http://www.sendspace.com/file/ayv2y0