Write SQL query to solve given problem: What is the average occurrence of the word "grec" on each Wikipedia page that has this word?. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT CAST(SUM(T2.occurrences) AS REAL) / COUNT(T1.wid) FROM words AS T1 INNER JOIN pages_words AS T2 ON T1.wid = T2.wid WHERE T1.word = 'grec'