Question: Calculate the percentage of households in residential areas of countries over 10000.
SQL: SELECT CAST(COUNT(CASE WHEN T2.households > 10000 THEN T1.zip_code ELSE NULL END) AS REAL) * 100 / COUNT(T1.zip_code) FROM country AS T1 INNER JOIN zip_data AS T2 ON T1.zip_code = T2.zip_code