2nd+Operations+and+Algebraic+Thinking

Operations and Algebraic Thinking 2.OA 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 //. // 2. Fluently add and subtract within 20 using mental strategies. By end of Grade 2, know from memory all sums of two one-digit numbers. 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. 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.
 * Represent and solve problems involving addition and subtraction. **
 * Add and subtract within 20. **
 * Work with equal groups of objects to gain foundations for multiplication. **