What is the average number of electorates (2003) reserved for sc with a constituency number of 50?
CREATE TABLE "assembly_segments" (
  "constituency_number" text,
  "name" text,
  "reserved_for_sc_st_none" text,
  "district" text,
  "number_of_electorates_2003" real
);
SELECT AVG("number_of_electorates_2003") FROM "assembly_segments" WHERE "reserved_for_sc_st_none"='sc' AND "constituency_number"='50';