Answer:
1/4 or 0.25 or 25%
Explanation:
Since there are 12 books total and 3 of them are mysteries, if you selected 12 books to read, 3 would be mysteries, therefore, theoretically, if you selected 4, one would be a mystery. 3/12 = 1/4
1/4 can also be written as 0.25 or 25%