Which Number of households has Per capita income of $21,571, and a Population smaller than 9,783?
CREATE TABLE "minnesota_counties_ranked_by_per_capita_" (
  "county" text,
  "per_capita_income" text,
  "median_household_income" text,
  "median_family_income" text,
  "population" real,
  "number_of_households" real
);
SELECT AVG("number_of_households") FROM "minnesota_counties_ranked_by_per_capita_" WHERE "per_capita_income"='$21,571' AND "population"<'9,783';