What year was the Competition of World Junior Championships with a 20th (qf) position?
CREATE TABLE "competition_record" (
  "year" real,
  "competition" text,
  "venue" text,
  "position" text,
  "event" text,
  "notes" text
);
SELECT AVG("year") FROM "competition_record" WHERE "competition"='world junior championships' AND "position"='20th (qf)';