SAT Question 2a08d878: Probability And Conditional Probability answer and explanation with Desmos solution

Choice B is correct. Since there are $n$ nonfiction and $12$ fiction books on the bookshelf, $n+12$ represents the total number of books. If one of these books is selected at random, the probability of selecting a nonfiction book is equivalent to the number of nonfiction books divided by the total number of books. Therefore, the probability of selecting a nonfiction book, in terms of $n$, is $\frac{n}{n+12}$.