CREATE TABLE table_42964 ("Year" FLOAT, "Result" FLOAT, "World Rank" TEXT, "Location" TEXT, "Date" TEXT)

What Year has a Result smaller than 20.31, and a World Rank of 5th?
SELECT AVG("Year") FROM table_42964 WHERE "Result" < '20.31' AND "World Rank" = '5th'
SELECT AVG("Year") FROM "table_42964" WHERE "Result" < '20.31' AND "World Rank" = '5th'