How many users from the group "F29-32" who were active in the events on 2016/5/7?
active users refers to is_active = '1'; on 2016/5/7 refers to timestamp = '2016/5/7 XX:XX:XX';
SELECT COUNT(T1.app_id) FROM app_events AS T1 INNER JOIN events AS T2 ON T1.event_id = T2.event_id INNER JOIN gender_age AS T3 ON T2.event_id = T3.device_id WHERE SUBSTR(T2.`timestamp`, 1, 10) = '2016-05-07' AND T1.is_active = '1' AND T3.`group` = 'F29-32'