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# Adding and Subtracting within 1000

## In this unit students •  work toward fluency with adding and subtracting within 100, mentally within 20; •  mentally add and subtract 10 or 100 to any number; •  add and subtract within 1000 using strategies based on place value and properties of operations; •  understand and explain addition and subtraction strategies; •  solve one- and two-step word problems, including word problems involving dollars and cents.

This unit circles back to addition and subtraction, extending this work to larger numbers. Building on units 2.2 and 2.3, students use strategies based on place value, properties of operations, and the relationship between addition and subtraction in order to add and subtract within 1000. Knowing the strategies is not enough; students must understand and explain their addition and subtraction strategies. The strategies students develop help them solve more sophisticated addition and subtraction problems, including ones with larger numbers, ones with more numbers (for example, adding four two-digit numbers instead of two), and word problems involving more than one step. Students continue to work toward fluency with adding and subtracting within 20 (mentally) and 100.

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