There are 320 popular science books in the school library, two thirds more than story books. How many story books are there?
There are 320 popular science books in the school library, two thirds more than story books, and 480 story books. According to relevant public information, there are 320 popular science books in the school library, so the number of story books is 320 times 3/2 equals 480, which means there are 480 story books.