List the educationnum and response of customers within the age of 20 to 30 that has the highest number of inhabitants among the group.
age of 20 to 30 refers to age BETWEEN 20 AND 30; the highest number of inhabitants refers to MAX(INHABITANTS_K);
SELECT T1.EDUCATIONNUM, T2.RESPONSE FROM Customers AS T1 INNER JOIN Mailings1_2 AS T2 ON T1.ID = T2.REFID INNER JOIN Demog AS T3 ON T1.GEOID = T3.GEOID WHERE T1.age >= 20 AND T1.age <= 30 ORDER BY T3.INHABITANTS_K DESC LIMIT 1