Among the professors with a teachability of 3 and below, what is the percentage of their student advisees with a low salary?
teachability < = 3; percentage = MULTIPLY(DIVIDE(COUNT(salary = 'low'), COUNT(salary)), 1.0);
SELECT CAST(SUM(CASE WHEN T1.salary = 'low' THEN 1 ELSE 0 END) AS REAL) * 100 / COUNT(T1.salary) FROM RA AS T1 INNER JOIN prof AS T2 ON T1.prof_id = T2.prof_id WHERE T2.teachingability < 3