He books in a private library are classified as fiction and nonfiction. There are 400 books in the library. There are 40 more fiction books than nonfiction books. Audrey randomly picks a book. A few minutes later, Ryan randomly picks one of the remaining books. What is the probability that both pick nonfiction books?

First, you have to set a system of equations to determine the number of fiction and of nonfiction books. Call f the number of fiction books and n the number of nonfiction books. Then 400 = f + n. And f = n + 40 = > n = f - 40 = > 400 = f + f - 40 = > 400 - 40 = 2f = > f = 360 / 2 = 180. Now to find the probability of picking two fiction books, take into account the the Audrey will pick from 180 fiction books out of 400, and Ryan will pick from 179 fiction books out of 399, so the probability will be (180 / 400) * (179/399) = 0.20 (rounded to two decimals). Answer: 0.20