Students measure and round to solve problems in Topics D and E (3.NBT.1, 3.MD.1, 3.MD.2). In these topics they use estimations to test the reasonableness of sums and differences precisely calculated using standard algorithms. From their work with metric measurement students have a deeper understanding of the composition and decomposition of units. They bring this to every step of the addition and subtraction algorithms with two- and three-digit numbers as 10 units are changed for 1 unit or 1 unit is changed for 10 units (3.NBT.2). Both topics end in problem solving involving metric units or intervals of time. Students round to estimate, and then calculate precisely using the standard algorithm to add or subtract two- and three-digit measurements given in the same units (3.NBT.1, 3.NBT.2, 3.MD.1, 3.MD.2).
Grade 3 Mathematics Module 2, Topic D, Overview
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