This Problem Set is a part of the Lesson 29, Unit 5, Grade 4. In this lesson, students use benchmark fractions and number lines to estimate the sum or difference of two mixed numbers by rounding each fraction, to round two mixed numbers to the nearest half or whole number and then find the sum, and to estimate the difference of two fractions greater than 1. Students then use benchmark numbers or mental math to estimate the sum and difference of two mixed numbers.