Put in =IF(AI2=0,0,AP2/(AI2*COUNTIF(AJ2:AL2,">0"))) in AQ2

But your question was...
a b c d e f g h i k l m n o p q r
0 0 0 4 3 0 0 0 4 5 0 0 0 0 0 2 ((4+3)/2) +((4+5)/2)