Question: Among the matches in 2013, what is the percentage of winning of the team "Mumbai Indians"?
SQL: SELECT CAST(SUM(CASE WHEN T2.Match_Winner = 7 THEN 1 ELSE 0 END) AS REAL) * 100 / COUNT(T2.Match_Winner) FROM Team AS T1 INNER JOIN Match AS T2 ON T1.Team_Id = T2.Match_Winner WHERE T2.Match_Date LIKE '2013%'