What is the average Total when silver is less than 1, and the rank is 15?
CREATE TABLE "medal_table" (
  "rank" text,
  "nation" text,
  "gold" real,
  "silver" real,
  "bronze" real,
  "total" real
);
SELECT AVG("total") FROM "medal_table" WHERE "silver"<1 AND "rank"='15';