NC.2.OA.1

Represent and solve addition and subtraction word problems, within 100, with unknowns in all positions, by using representations and equations with a symbol for the unknown number to represent the problem, when solving:

One-Step problems:
- Add to/Take from - Start Unknown
- Compare - Bigger Unknown
- Compare - Smaller Unknown
Two-Step problems involving single digits:
- Add to/Take from-Change Unknown
- Add to/Take From-Result Unknown

Step 1: Lesson Standards & Learning Goals

Unpacking Clarification

In Grade 2, students continue to work with problem types from previous grade levels (Result Unknown and Change Unknown) with numbers less than 100. Second graders are expected to independently read, represent with manipulatives or pictures, write equations, and solve all addition and subtraction problem types, with unknowns in all positions. Students begin exploring, representing, and solving word problems aligned to the four remaining problem types:

• Add To/Start Unknown • Take From/Start Unknown • Compare/Bigger Unknown • Compare/Smaller Unknown

The introduction of new problem types should begin by providing students with opportunities to explore word problems with numbers less than 10 initially so that they can represent them with manipulatives and/or pictures.

Compare problems provide opportunities for students to reason about which quantity is smaller and larger, which influences whether students should add or subtract. The use of keywords to determine operations should not be used since it will lead students to do the wrong operation in Second Grade and future years. Alternatively, students should use part-part-whole diagrams, bar models, and/or reasoning about the size of quantities while solving compare problems.

Two-step problems should involve single-digit addends so the primary focus is on understanding the problem situation and finding strategies to solve the problem. One-step word problems use one operation. Two-step word problems use two operations which may include the same operation or opposite operations. As second-grade students solve one- and two-step problems they use manipulatives such as snap cubes, place value materials, ten frames, etc.; create drawings of manipulatives to show their thinking; or use number lines to solve and describe their strategies. They then relate their drawings and materials to equations.

Second graders use a variety of strategies, such as making tens and using fluency strategies such as doubles and near doubles, to help solve problems involving addition and subtraction within 20. With larger numbers, students are expected to apply their understanding of place value to solve problems using strategies such as adding or subtracting by place value, representing addition and subtraction on a number line, or by using base ten blocks or drawings of base ten blocks.

Sample Essential Questions

What are the steps for solving a one or two-step word problem?
How can manipulatives and drawings be used to represent word problems?
What strategies can be used to solve one and two-step word problems?
What are ways to distinguish between addition and subtraction problems?

Vocabulary

add
compare
difference
equal sign
equation
fewer/fewer than
less/less than
more/more than
position
representation
subtract
sum
unknown number

Students will be able to...

Read, represent with manipulatives or pictures, write equations, and solve all addition and subtraction problem types, with unknowns in all positions.
- - Use manipulatives, drawings, and equations with a symbol (box or blank) for the unknown number to solve word problems.
Reason about which quantity is smaller and larger when solving compare problems
- - Use part-part-whole diagrams, bar models, and/or reasoning about the size of quantities while solving compare problems.
Use a variety of strategies to solve one and two-step word problems.

Students will know...

An equation is a number sentence with an equal sign.
The equal sign means equivalent or having the same value.
An unknown can be in any position in an equation.
A box, blank, or a picture can be used to represent the unknown number in an equation.

Step 2: Assessment