Mary was working on a research paper and already had borrowed 5 books from the library. 3 books weren't helpful so she returned those and checked out 5 more books. 3 days later, she went back to the library and returned 2 of those books and checked out 7 more books. How many books does Mary currently have checked out of the library? Let's answer step by step:
Mary started with 5 books and returned 3 so she had 5 - 3 = 2 books. She had 2 books and checked out 5 more books so she had 2 + 5 = 7 books. She now has 7 books but returned 2 so she has 7 - 2 = 5 books. She had 5 books and checked out 7 more books so she has 5 + 7 = 12 books checked out. The answer: 12.