This document provides a summary of Chapter 15 from a mathematics textbook. The chapter covers adding and subtracting decimals through 6 lessons: 1) rounding decimals, 2) estimating decimal sums and differences, 3) using a problem-solving strategy of working backward, 4) adding decimals, 5) choosing a problem-solving strategy, and 6) subtracting decimals. Each lesson includes examples and practice problems to illustrate the concepts and build skills in adding and subtracting decimals.