# 1.OA.A.1

Use addition and subtraction within 20 to solve word problems involving situations of adding to, taking from, putting together, taking apart, and comparing, with unknowns in all positions, e.g., by using objects, drawings, and equations with a symbol for the unknown number to represent the problem.1

## Summary:

This standard emphasizes a student’s ability to not only understand the meaning of addition and subtraction, but to demonstrate that knowledge within word problems involving situations within 20. 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 as well.

## Understanding the Standard:

• When reading through a word problem, students need to represent the problem using objects, drawings, and equations. A symbol such as a box or question mark are appropriate at this level. However, remind students to read the entire problem to be sure they understand what they are really being asked to do and that they don't get tricked by a word.
• Students need guidance in deciding if the answer they have computed makes sense.
• Students should justify their approach to solving the problem in a variety of ways.
• Students should be able to use an equation with a symbol representing an unknown number to represent a given situation.
• Problems such as 5+?=4+8 are good examples and can be modeled with blocks or other counters. The idea is to get students to think about an equal sign as “is the same as.” This will aid in developing the idea of an equation as something that is balanced.
• A balance beam with numbers on each side allows a physical example of number equations. Several companies sell this item under the name “math balance with weights.”

## Questions to Focus Instruction:

• Can students represent an addition problem, with numbers within 20, with an unknown using objects? Using drawings? Using equations with a symbol?
• Can students represent a subtraction problem, with numbers within 20, with an unknown using objects? Using drawings? Using equations with a symbol?

## Skills

Prior to: Students can assign a numerical value to a group of sorted objects. Students understand the concepts involving putting together or taking apart. In an oral word problem, students can summarize the main idea of the problem and with teacher guidance, assign numeric values to important information within the word problem. Go to K.OA.A.2 to see previous skills in this progression.

At Grade Level: Students are able to read a mathematical word problem and decide if addition or subtraction should be used to solve it. Students are able to identify relevant information and assign a numeric value to all known information, and assign a variable to the unknown. Students can employ a variety of strategies for problem-solving and visually present the problem with drawings, pictures or models. Students are able to write the numeric sentence that will be used to guide their thinking and solving, including when the unknown portion is situated in a place other than the answer position.

Moving Beyond:
Students will use their mastery of prior skills to assign values for more complex word problems, even some involving two-step solutions. Go to 2.OA.A.1 to see the progression of related skills.

1 See Glossary, Table 1.