Calculate the percentage of recipes with no cholesterol included and have a cooking time less than 20 minutes among all recipes.
no cholesterol refers to cholestrl = 0; cooking time less than 20 minutes refers to cook_min < 20; calculation = MULTIPLY(DIVIDE(COUNT(cholestrl = 0 THEN recipe_id), COUNT(recipe_id)), 100)
SELECT CAST(SUM(CASE WHEN T1.cook_min < 20 AND T2.cholestrl = 0 THEN 1 ELSE 0 END) AS REAL) * 100 / COUNT(*) FROM Recipe AS T1 INNER JOIN Nutrition AS T2 ON T1.recipe_id = T2.recipe_id