CREATE TABLE table_203_82 (id DECIMAL, "first issued" DECIMAL, "design" TEXT, "slogan" TEXT, "serial format" TEXT, "serials issued" TEXT, "notes" TEXT)

what is the average serial format of the arizona license plates ?
SELECT "serial format" FROM table_203_82 GROUP BY "serial format" ORDER BY COUNT(*) DESC LIMIT 1
SELECT "serial format" FROM "table_203_82" GROUP BY "serial format" ORDER BY COUNT(*) DESC NULLS LAST LIMIT 1