Write SQL query to solve given problem: What is the ratio of professors and students?. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT CAST(SUM(CASE  WHEN professor = 1 THEN 1 ELSE 0 END) AS REAL) * 100 / SUM(CASE  WHEN student = 1 THEN 1 ELSE 0 END) AS per FROM person