Question: Among the universities in United States of America, what is the percentage of female students in year 2016?
SQL: SELECT SUM(CAST(T2.pct_female_students * T2.num_students AS REAL) / 100) * 100 / SUM(T2.num_students) FROM university AS T1 INNER JOIN university_year AS T2 ON T1.id = T2.university_id INNER JOIN country AS T3 ON T3.id = T1.country_id WHERE T3.country_name = 'United States of America' AND T2.year = 2016