Unit 1

Sums and Differences to 20

Grade 2
Math
    

 

Unit Length and Description:

 

20 days

 

From Grade 1, students have fluency of addition and subtraction within 10 and extensive experience working with numbers to 100. Unit 1 of Grade 2 reviews and extends addition and subtraction strategies that will help to provide each student with practice to achieve mastery of the new required fluencies (i.e., adding and subtracting within 20 and within 100) by the end of the year. Students learn to represent and solve word problems using addition and subtraction: a practice that will also continue throughout the year.

 

Standards:

 

OA - Operations and Algebraic Thinking

Represent and solve problems involving addition and subtraction.

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.

Add and subtract within 20.

2.OA.B.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.

NBT – Number and Operation in Base Ten

Use place value understanding and properties of operations to add and subtract.

2.NBT.B.5

Fluently add and subtract within 100 using strategies based on place value, properties of operations, and/or the relationship between addition and subtraction.

2.NBT.B.6

Add up to four twodigit numbers using strategies based on place value and properties of operations.

Standards for Mathematical Practice

1. Make sense of problems and persevere in solving them.

2. Reason abstractly and quantitatively.

3. Construct viable arguments and critique the reasoning of others.

4. Model with mathematics.

5. Use appropriate tools strategically.

6. Attend to precision.

7. Look for and make use of structure.

8. Look for and express regularity in repeated reasoning.

 

Instructional Outcomes

·         2.OA.1:

o   I can identify the number of steps to solve a word problem.

o   I can identify an unknown number in an equation using addition and subtraction up to 100.

o   I can identify the strategy/strategies for solving word problems. (Is it addition or subtraction?)

·         2.OA.2:

o   I can know from memory all sums and differences of 2 one-digit numbers within 20.

o   I can use mental strategies to add and subtract fluently within 20.

·         2.NBT.5:

o   I can identify the order in which to add three-digit numbers. (e.g. adding right to left)

o   I can identify properties of operations to add. (e.g. associative and commutative properties)

o   I can identify properties of operations to subtract. (e.g. associative and commutative properties)

·         2.NBT.6

o   I can identify strategies for adding up to four two-digit numbers based on place value.

 

Enduring Understandings:

 

·         I can think about numbers in different ways.

·         I can show numbers in all kinds of ways.

·         Knowing about numbers helps me answer everyday questions, such as, “how many” and “how much”.

·         There is more than one way to solve a problem.

·         Addition and subtraction are opposite operations.

·         I can compose and decompose a number.

·         Knowing my basic facts helps me to solve other problems.

Essential Questions:

 

·         What are different ways we can show or make (represent) a number?

·         Why do I use numbers to show “how much” and “how many”?

·         How can I solve the same problem in more than one way?

·         How are addition and subtraction opposite operations?

·         How can I compose and decompose a number?

·         How can I use the basic facts to solve other problems?