Question: Among the matches held in Mumbai, how many percent of them were held in Wankhede Stadium?
SQL: SELECT CAST(SUM(CASE WHEN T2.Venue_Name = 'Wankhede Stadium' THEN 1 ELSE 0 END) AS REAL) * 100 / COUNT(T3.Match_Id) FROM City AS T1 INNER JOIN Venue AS T2 ON T2.City_Id = T1.City_Id INNER JOIN Match AS T3 ON T3.Venue_Id = T2.Venue_Id WHERE T1.City_Name = 'Mumbai'