In female students in year 2012, how many of them from a state with number of schools ranges from 10 to 20?
female refers to gender = 'F'; number of schools refers to schools_count; schools_count BETWEEN 10 AND 20;
SELECT COUNT(T2.race) FROM state_sector_details AS T1 INNER JOIN state_sector_grads AS T2 ON T2.stateid = T1.stateid WHERE T2.gender = 'F' AND schools_count BETWEEN 10 AND 20 AND T2.year = 2012