Which Ratio has a Similar ISO A size of a3?
CREATE TABLE "ansi_paper_sizes" (
  "name" text,
  "in_in" text,
  "mm_mm" text,
  "ratio" real,
  "similar_iso_a_size" text
);
SELECT AVG("ratio") FROM "ansi_paper_sizes" WHERE "similar_iso_a_size"='a3';