Column A Column B Column C
100 100 =Sum(A1+B1)/2
100 =Sum(A1+B1)/2
100 100 =Sum(A1+B1)/2


As above i've two columns both with numbers in - i need to add them together and then divide by 2 - however column a and column b may not have a number in so results for above with my formula would be:

C1 100
C2 50
C3 100

and I want them to show:

C1 100
C2 100
C3 100


Thanks.