This Problem Set is part of the the Lesson 11, Unit 2, Grade 5. Look at #1a and 1b. What do you notice about the problems and their solutions? Look at #1f. If I got 800, what mistake did I make? Look at #3. Who was correct? What error did the other person make? Look at #4b and 4c. Do you think the actual quotients would be greater or less than the estimate?