In this lesson, students discuss solution strategies as they solve "take from with result unknown" and "take apart with addend unknown" word problems. (For example, "Colby is reading a book that is 14 pages long. She has already read 8 pages. How many more pages does Colby need to read to finish the book?") Students ask each other, "How and why did you solve it this way?" and then discuss which strategies are the most efficient.