How many distinct delegates are from counties with population larger than 50000?
SELECT count(DISTINCT T2.Delegate) FROM county AS T1 JOIN election AS T2 ON T1.County_id  =  T2.District WHERE T1.Population  >  50000
distinct delegates = COUNT(DISTINCT column_name); population larger than 50000 refers to Population > 50000; counties are related to election districts through county_id and district;