Explain simply why 220 is the correct answer to: Roselyn gives Mara three times as many books as she gives Rebecca and remains with 60 books. If Rebecca received 40 books, how many books did Roselyn have before?. Explanation:
If Roselyn gave Rebecca 40 books, and Mara was given three times as many books, Mara has 3 * 40 = 120 books. Rebecca and Mara's total number of books is 120 + 40 = 160 books. If Roselyn gave Mara and Rebecca her books, which is 160, then she initially had 60 + 160 = 220 books.