What percentage of streets named 11th Street are in Alameda County?
street named 11th Street refers to street_name = '11th st'; percentage = divide(count(street_name = '11th st' and County = 'alameda county'), count(street_name where County = 'alameda county')) * 100%
SELECT CAST(SUM(IIF(T1.street_name = '11th st', 1, 0)) AS REAL) * 100 / COUNT(T1.id_restaurant) FROM location AS T1 INNER JOIN geographic AS T2 ON T1.city = T2.city WHERE T2.County = 'alameda county'