What Year has a Result smaller than 20.31, and a World Rank of 5th?
CREATE TABLE "200_meters" (
  "year" real,
  "result" real,
  "world_rank" text,
  "location" text,
  "date" text
);
SELECT AVG("year") FROM "200_meters" WHERE "result"<20.31 AND "world_rank"='5th';