# Domain 2.OA, Operations and Algebraic Thinking

## Cluster 2.OA.A, Represent and solve problems involving addition and subtraction.

### Standard 2.OA.A.1

Use addition and subtraction within 100 to solve one- and two-step word problems involving situations of adding to, taking from, putting together, taking apart, and comparing, with unknowns in all positions, e.g., by using drawings and equations with a symbol for the unknown number to represent the problem.

## Cluster 2.OA.B, Add and subtract within 20.

### Standard 2.OA.B.2

Fluently add and subtract within 20 using mental strategies (See standard 1.OA.6 for a list of mental strategies). By end of Grade 2, know from memory all sums of two one-digit numbers.

## Cluster 2.OA.C, Work with equal groups of objects to gain foundations for multiplication.

### Standard 2.OA.C.3

Determine whether a group of objects (up to 20) has an odd or even number of members, e.g., by pairing objects or counting them by 2s; write an equation to express an even number as a sum of two equal addends.

### Standard 2.OA.C.4

Use addition to find the total number of objects arranged in rectangular arrays with up to 5 rows and up to 5 columns; write an equation to express the total as a sum of equal addends.