# 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.1

*TNCore Focus Standard

## Summary:

This standard emphasizes a student’s ability to not only understand the meanings of addition and subtraction through 100, but also demonstrate that knowledge within word problems. Students will further demonstrate this knowledge by modeling each situation with number sentences and drawings. Additionally, students can solve for any unknown quantity in a problem involving addition and/or subtraction. At this point, students are expected to work one- or two-step word problems.See table for suggestions: Addition Subtraction table.docx

## Understanding the Standard:

• See the table link above for illustrations of all of the approaches this standard requires. Teachers should adjust the size of the numbers in the problems within 100. All numbers in the problem, including intermediate calculations and the answer, must be within 100.
• In grade 2, drawing strategies will change from earlier grades since numbers are larger. One way students can adapt drawings to larger numbers is to use bar models. For example, suppose that I know that I now have 80 cows on a farm. I received 25 of those cows last week, and I want to know how many cows I had before that. I can draw a rectangle with a question mark representing cows I had before I received the 25, and then another adjacent rectangle with a 25 in it representing the cows I just received. I know that the two rectanlges needs to "contain" 80 cows, so the unknown box needs to "contain" 80 - 25 = 55 cows.
• When reading through a word problem, students will become familiar with language like "altogether", "sum", and "in all" - learning the language of mathematics is part of the work of learning mathematics.
• When giving word problems, include two-step word problems that involve both addition and subtraction. Bar models and line graphs may help students visualize word problems.
• Consult the table on page 88 of the CCSSM and make a conscious effort to give students problems that represent a variety of problem types in the table.

## Questions to Focus Instruction:

• Can students identify whether to use addition or subtraction within 100 to solve the word problem and represent it with an algebraic equation?
• Can students justify which operation(s) they used when solving a problem?
• Can students use a symbol for the unknown quantity in a problem?
• Given an equation involving addition or subtraction with an unknown in any position, can students determine the unknown?
• Can students solve one- and two-step word problems?

## Skills:

Prior to: Students can add within 100. Students are able to read a mathematical word problem and decide if addition or subtraction should be used to solve the problem. Students are able to identify relevant information and assign a numeric value to all important information. Students can employ a variety of strategies for problem-solving and visually present the problem with drawings, pictures or models. Go to 1.OA.A.1 to see previous skills in this progression.