What is the percentage of establishments with a risk level of 1 among all of the establishments that passed the inspection?
a risk level of 1 refers to risk_level = 1; pass the inspection refers to results = 'Pass'; percentage = divide(sum(license_no where risk_level = 1), count(license_no)) * 100% where results = 'Pass'
SELECT CAST(COUNT(CASE WHEN T1.risk_level = 1 THEN T1.license_no END) AS REAL) * 100 / COUNT(T1.license_no) FROM establishment AS T1 INNER JOIN inspection AS T2 ON T1.license_no = T2.license_no WHERE T2.results = 'Pass'