How many students live there?
SELECT COUNT ( T1.stuid )  FROM lives_in AS T1 JOIN dorm AS T2 ON T1.dormid  =  T2.dormid WHERE T2.student_capacity   =    ( SELECT max ( student_capacity )  FROM dorm ) 
counting the number of students living in the place with the maximum student capacity refers to using COUNT on student IDs after joining tables based on dorm IDs and filtering for the dorm with the maximum student capacity.