Instances in which A1:A2793 read "A1" AND in which the numerical value in C1:C2793 is >50.
By "read A1" do you mean cell A1? (I'm being too literal probably, but you don't mean the text "A1"?)

=SUMPRODUCT(($A$1:$A$2793=$A$1)*((COUNTIF(C1:C2793,">50")/(COUNTIF(C1:C2793,">50")))))