Addition and Subtraction and Number System Throughout this school year, students will work on making sense of the action of different types of addition and subtraction problems. They will develop efficient strategies for solving them and for recording their work. They solve addition and subtraction problems in ways that make sense to them and practice using particular strategies. Students study two particular strategies for addition –adding tens and ones and adding one number in parts. By the end of the school year, students are expected to have at least one strategy that they can use to accurately and efficiently solve an addition problem. In Grade One, students’ work with place value becomes the basis for the development of strategies for adding and subtracting 2-digit numbers. The two strategies for addition, adding by place and adding one number in parts, and the strategy for subtraction of subtracting one number in parts, depend on an understanding of how to break numbers into tens and ones.
Benchmarks (compiled from Units 1, 3, and 8) • Determine the difference between two numbers (up to 45) • Interpret addition and subtraction story problems (read a story problem and determine what needs to be figured out) • Have at least one strategy for solving addition and subtraction (as removal) story problems • Demonstrate fluency with addition combinations to 10 + 10 • Understand what it means to double a quantity • Use known combinations to add several numbers in any order • Interpret and solve subtraction (removal) and unknown change story problems with totals up to 45 • Count on or break numbers apart to add two or more numbers up to a total of 45 • Write an equation that represents an addition or subtraction situation • Determine the difference between a number and any multiple of 10 up to 100 • Add multiples of 5, up to 100 • Subtract two-digit numbers • Reason about partners, teams, and leftovers to make and justify generalizations about what happens when even and odd numbers are added • Add two 2-digit numbers accurately and efficiently