Topic D focuses on the application of the tools and concepts presented in Topics A through C. Students synthesize their understanding of addition and subtraction strategies and then use that understanding to determine which of those strategies to apply to a variety of problems, including number bond problems and problems with the unknown in all positions (e.g., 200 + ____ = 342 or ____ – 53 = 400).
Students then discuss and analyze their chosen methods and determine which method is most efficient for the given problem type. For example, when digits are close to the next ten or hundred (e.g., 530 – ____ = 390), some students might use related addition and mentally add on tens and hundreds, while others might solve the same problem using arrow notation.
Working with these problems provides a sound foundation for future work with word problems. Listening to peer explanations can make certain strategies more accessible for students who struggle; it also allows for more time and practice to achieve mastery.
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