Students identify relevant and missing information, choose addition or subtraction, represent situations with objects, drawings, number lines, models, tables, and equations, and solve whole-number problems within 1,000, including simple two-step problems within 100. They compare and explain strategies, organize work systematically, justify comparisons through 1,000 using place value, create stories for addition and subtraction equations within 100, and explain solutions in words for addition, subtraction, measurement, equal-group, and sharing situations. They check calculations using inverse operations and estimation, find and correct addition and subtraction errors involving regrouping, make reasonable conjectures from patterns and examples, and use logical elimination to identify possible solutions.