which # / county is correct for year less than 1981 and chalmers as location?
CREATE TABLE "membership" (
  "school" text,
  "location" text,
  "mascot" text,
  "num_county" text,
  "ihsaa_class" text,
  "year_joined" real,
  "previous_conference" text
);
SELECT "num_county" FROM "membership" WHERE "year_joined"<1981 AND "location"='chalmers';