CREATE TABLE table_70036 ("Name" TEXT, "Years" TEXT, "Gender" TEXT, "Area" TEXT, "Authority" TEXT, "Decile" FLOAT, "Roll" FLOAT)

How many decile has a roll less than 20?
SELECT AVG("Decile") FROM table_70036 WHERE "Roll" < '20'
SELECT AVG("Decile") FROM "table_70036" WHERE "Roll" < '20'