How many female users use ZenFone 5 devices?
female refers to gender = 'F'; ZenFone 5 refers to device_model = 'ZenFone 5';
SELECT COUNT(T1.gender) FROM gender_age AS T1 INNER JOIN phone_brand_device_model2 AS T2 ON T2.device_id = T1.device_id WHERE T1.gender = 'F' AND T2.device_model = 'ZenFone 5'