human
Five years ago, there were 500 old books in the library. Two years ago, the librarian bought 300 books. Last year, the librarian bought 100 more books than she had bought the previous year. This year, the librarian donated 200 of the library's old books. How many books are in the library now?
assistant
How many books did the librarian buy last year? ** Last year the librarian bought 300 + 100 = <<300+100=400>>400 books.
How many books were in the library as of last year? ** Thus, there were 500 + 300 + 400 = <<500+300+400=1200>>1200 books as of last year.
How many books are in the library now? ** Therefore, there are 1200 - 200 = <<1200-200=1000>>1000 books now in the library.
#### 1000