Lizzy: Lidia has a collection of books. Her collection is four times bigger than the collection which her friend Susan has. In total Susan and Lidia, both have 3000 books. How many books does Susan have in her collection?.
Me: Hmmm, let me think. I think this is the detailed solution:
Let x be the number of books in Susan's collection. The collection of both Susan and Lidia would then be 4 * x + x = 3000. 5 * x = 3000. x = 600. Final answer: 600.