Among the female users that uses OPPO as their phone brand, what is the percentage of them of the user that uses R815T model to install the app?
female refers to gender = 'F'; percentage = DIVIDE(SUM(IF(phone_brand = 'OPPO',1,0)), SUM(IF(device_id = 'R815T',1,0))); R815T refers to device_id = 'R815T';
SELECT SUM(IIF(T1.phone_brand = 'OPPO', 1, 0)) / SUM(IIF(T1.device_id = 'R815T', 1, 0)) AS num FROM phone_brand_device_model2 AS T1 INNER JOIN gender_age AS T2 ON T1.device_id = T2.device_id WHERE T2.gender = 'F'