Average IF MOD - Stuck?

Hi,

Trying to design a student grade / level sheet for my school department.

Basically need to average results from every other coloumn across a row, but need to find from two alternate coloumns and combination. Thought I had it but now given up.

Could some kind soul check attached and correct my Array Formula from cell O4, P4 and Q4 have spun myself into a knot over this, it should be so simple!

Appreciate any help

Thanks

Dave

=AVERAGE(IF(MOD(COLUMN(C4:N4),2)=1,IF(C4:N4<>0,C4:N4)))