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```
SELECT ROUND(COUNT(t2.player_id)/COUNT(t1.player_id),2) AS fraction
FROM
(SELECT player_id, MIN(event_date) AS first_login FROM Activity GROUP BY player_id) t1 LEFT JOIN Activity t2
ON t1.player_id = t2.player_id AND t1.first_login = t2.event_date - 1
```
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