Answer:
[tex]\frac{29}{65}[/tex]
Step-by-step explanation:
Since there are 54 students who read either fiction or non-fiction, 40 students who read fiction, and 43 students who read non-fiction, there are [tex]40+43-54=29[/tex] students who read both fiction and non-fiction.
There are 65 students in the library, so the probability a random-selected student will have read both fiction and non-fiction is [tex]\fbox{$\frac{29}{65}$}[/tex].