Question: What is the percentage of device users in the F27-28 age group who experienced an event on the 3rd of May 2016?
SQL: SELECT SUM(IIF(T1.`group` = 'F27-28', 1, 0)) / COUNT(T1.device_id) AS per FROM gender_age AS T1 INNER JOIN events_relevant AS T2 ON T1.device_id = T2.device_id WHERE SUBSTR(T2.timestamp, 1, 10) = '2016-05-03'