# Adding and Subtracting within 100.

## In this unit students •  work toward fluency with adding and subtracting within 100, mentally within 20; •  use number lines to represent sums and differences within 100; •  understand and explain addition and subtraction strategies; •  solve one- and two-step word problems, including word problems involving pennies and dimes, and using information represented in picture and bar graphs.

In this unit students begin by revisiting the work they did in first grade with addition and subtraction. Working on addition and subtraction in the early part of the year maximizes the time students have to develop fluency with these operations (2.OA.B.2 and 2.NBT.B.5).

Students use number lines to represent sums and differences within 100, allowing them to develop a more abstract understanding of these operations. They add and subtract using strategies based on the properties of addition and the relationship between addition and subtraction. It is important for students to articulate and explain their addition and subtraction strategies.

Students solve one- and two-step word problems involving addition and subtraction, including problems with pennies and dimes, and problems with lengths measured in the same units.

Bar graphs and picture graphs support the major work of second grade by asking students to solve put-together and take-apart problems using information presented in graph(s). These are examples of how coherence builds across different domains within a single grade.

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