Excel 2007 : Applying same formula after nth rows with skipping some rows in between

I want to apply same formulas in a particular row after jumping some rows.For example
particle 1 will give new particle 1' when N4 =0.5*(c4+50) but N5 =0.5*(c5+0)..

Similarly N12=0.5*(c12+50)..But N13 =0.5*(c13+0)..


Can anyone plese help me how to copy formula from N4 to N12 without including N5.

I have also attached th jpg file..Please Help!!!!!!!!

PARTICLE 1


X 50 90 Y 50 0 0
0 60 0 100 50




PARTICLE 2


X 0 140 Y 0 0 0
0 60 50 100 50




PARTICLE 3

X 60 80 Y 0 60 0
0 60 50 40 50

Hi,

Try this:

1. Select cells N4 and N5.

2. Click the copy button (or use Ctrl-C).

3. Select cell N12.

4. Click the paste button (or use Ctrl-V).

Cheers,