This Problem Set is a part of the Lesson 17, Unit 2, Grade 3. In this lesson, students estimate the sums of two numbers by rounding both addends to either the nearest ten or hundred, and then compare their estimates to the actual sum. For example, they estimate 362 + 159 by rounding to the nearest hundred (400 + 200 = 600) and rounding to the nearest ten (360 + 160 = 520). Then they calculate the actual sum and determine which estimating method was more accurate.