This formula is complicated and very specific to your description, but it
should accruately calculate the weighted average of the assignments that do
not have a blank in row 5:
=SUMPRODUCT(--(B5
5),(B2
2))/(IF(ISBLANK(B5),0,B2)+IF(ISBLANK(C5),0,C2)+IF(ISBL ANK(D5),0,D2))