Elementary Mathematics

1st Grade Unit 3 Overview and Standards


Use these links to access resources for this unit.


 Before You Begin this Unit…   Unit at a Glance

In Grade K, students had experience with addition and subtraction situations within 10.  In Grade 1, students work with addition and subtraction situations within 20 (10+10=20) to continue to better understand the operations and how to apply the operations to problem solving.  Students in Grade 1 are introduced to comparison subtraction.  The modeling of comparison subtraction is different from the other two types of subtraction.  Instead of finding part of one group as in take-away or part-whole subtraction, students model the two groups represented by the minuend and subtrahend and find the difference between the two.  Students are also introduced to using a symbol as an unknown, though students have used answer blanks or answer boxes as informal symbols for unknowns in the past. 

Throughout first grade, students work with the important idea that quantities can be composed and decomposed in different ways while the total quantity remains the same.  Students have repeated experiences breaking one number, a whole, into two parts or combining two parts to form a whole.  They begin to notice that as one part increases, the other part decreases, while the whole remains the same, i.e., if 3 + 6 = 9, then 4 + 5 = 9 as well.  Teachers need to assess students’ developing understanding of this concept and students’ strategies for solving problems like these.

As first grade students work with story problems, they should visualize the action of story problems and solve the problems in ways that make sense to them.  Students use mathematical tools and representations to model and solve addition and subtraction problems and to clarify and communicate their thinking.  They are encouraged to represent their work on paper and may use a combination of pictures, words, numbers, and mathematical symbols.  In this unit, students move beyond solving addition story problems to problems that involve subtraction or missing addends.  Teachers need to assess students’ ability to interpret and solve addition, subtraction, and missing addend story problems.

Also, students are introduced to Today’s Number in which they generate many ways to make a given number.  Students can write expressions that have more than two addends and that use addition, subtraction, or even addition and subtraction.

Students may discover ways to use one expression to generate another or find patterns that help them generate many expressions. Teachers need to assess students’ flexibility in composing and decomposing numbers, their ability to use previous expressions and patterns to generate other expressions, the size of the numbers students are comfortable working with, and the operations they are comfortable using.

In investigation 4, students work on counting in a variety of ways.  They are expected to learn the rote counting sequence to 100 and beyond, to read and write numbers to 105, and strategies for counting groups of objects.  By the end of this unit, students are expected to be able to read, write, and record numbers up to 65 and to count a set of 40 to 50 objects accurately.   Teachers need to assess how high students can count, what numbers students can read and write, and whether students can accurately count a set of 40 to 50 objects.

Suggested Dates:

October 29-December 12

Estimated Duration:

28 Days

Investigation 1: 10 lessons (include 1.10A)

Investigation 2: 3 lessons

Investigation 3: 5 lesson

Investigation 4: 8 lessons

 Standards Addressed in the Unit

Click here for the NCDPI CCSS Unpacking Document

Unit Goals:    

• Find at least 5 combinations of 2 addends for a number up to 15.

• Combine 2 small quantities.

• Interpret (retell the action and sequence) and solve addition and subtraction story problems.

• Subtract one small quantity from another.

• Represent numbers by using equivalent expressions.

• Count a set off 40 – 50 objects.

• Rote count, read, and write numbers to 65.

This unit focuses on the Operations and Algebraic thinking strand. For more information about this strand and how it should look in the classroom, please visit the Common Core State Standards video series or the Link to unpacking document.

Represent and solve problems involving addition and subtraction.

1.OA.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.OA.2. Solve word problems that call for addition of three whole numbers whose sum is less than or equal to 20, e.g., by using objects, drawings, and equations with a symbol for the unknown number to represent the problem.

Understand and apply properties of operations and the relationship between addition and subtraction.

1.OA.3. Apply properties of operations as strategies to add and subtract.2 Examples: If 8 + 3 = 11 is known, then 3 + 8 = 11 is also known. (Commutative property of addition.) To add 2 + 6 + 4, the second two numbers can be added to make a ten, so 2 + 6 + 4 = 2 + 10 = 12. (Associative property of addition.)

1.OA.4. Understand subtraction as an unknown-addend problem. For example, subtract 10 – 8 by finding the number that makes 10 when added to 8. Add and subtract within 20.

Add and subtract within 20.

1.OA.5. Relate counting to addition and subtraction (e.g., by counting on 2 to add 2).

1.OA.6. Add and subtract within 20, demonstrating fluency for addition and subtraction within 10. Use strategies such as counting on; making ten (e.g., 8 + 6 = 8 + 2 + 4 = 10 + 4 = 14); decomposing a number leading to a ten (e.g., 13 – 4 = 13 – 3 – 1 = 10 – 1 = 9); using the relationship between addition and subtraction (e.g., knowing that 8 + 4 = 12, one knows 12 – 8 = 4); and creating equivalent but easier or known sums (e.g., adding 6 + 7 by creating the known equivalent 6 + 6 + 1 = 12 + 1 = 13).

 Work with addition and subtraction equations.

1.OA.7. Understand the meaning of the equal sign, and determine if equations involving addition and subtraction are true or false. For example, which of the following equations are true and which are false? 6 = 6, 7 = 8 – 1, 5 + 2 = 2 + 5, 4 + 1 = 5 + 2.

1.OA.8. Determine the unknown whole number in an addition or subtraction equation relating three whole numbers. For example, determine the unknown number that makes the equation true in each of the equations 8 + ? = 11, 5 = _ – 3, 6 + 6 = _.

Unit Goals:    

• Find at least 5 combinations of 2 addends for a number up to 15.

• Combine 2 small quantities.

• Interpret (retell the action and sequence) and solve addition and subtraction story problems.

• Subtract one small quantity from another.

• Represent numbers by using equivalent expressions.

• Count a set off 40 – 50 objects.

• Rote count, read, and write numbers to 65.

This unit focuses on the Operations and Algebraic thinking strand. For more information about this strand and how it should look in the classroom, please visit the Common Core State Standards video series or the Link to unpacking document.

Represent and solve problems involving addition and subtraction.

1.OA.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.OA.2. Solve word problems that call for addition of three whole numbers whose sum is less than or equal to 20, e.g., by using objects, drawings, and equations with a symbol for the unknown number to represent the problem.

Understand and apply properties of operations and the relationship between addition and subtraction.

1.OA.3. Apply properties of operations as strategies to add and subtract.2 Examples: If 8 + 3 = 11 is known, then 3 + 8 = 11 is also known. (Commutative property of addition.) To add 2 + 6 + 4, the second two numbers can be added to make a ten, so 2 + 6 + 4 = 2 + 10 = 12. (Associative property of addition.)

1.OA.4. Understand subtraction as an unknown-addend problem. For example, subtract 10 – 8 by finding the number that makes 10 when added to 8. Add and subtract within 20.

Add and subtract within 20.

1.OA.5. Relate counting to addition and subtraction (e.g., by counting on 2 to add 2).

1.OA.6. Add and subtract within 20, demonstrating fluency for addition and subtraction within 10. Use strategies such as counting on; making ten (e.g., 8 + 6 = 8 + 2 + 4 = 10 + 4 = 14); decomposing a number leading to a ten (e.g., 13 – 4 = 13 – 3 – 1 = 10 – 1 = 9); using the relationship between addition and subtraction (e.g., knowing that 8 + 4 = 12, one knows 12 – 8 = 4); and creating equivalent but easier or known sums (e.g., adding 6 + 7 by creating the known equivalent 6 + 6 + 1 = 12 + 1 = 13).

Work with addition and subtraction equations.

1.OA.7. Understand the meaning of the equal sign, and determine if equations involving addition and subtraction are true or false. For example, which of the following equations are true and which are false? 6 = 6, 7 = 8 – 1, 5 + 2 = 2 + 5, 4 + 1 = 5 + 2.

1.OA.8. Determine the unknown whole number in an addition or subtraction equation relating three whole numbers. For example, determine the unknown number that makes the equation true in each of the equations 8 + ? = 11, 5 = _ – 3, 6 + 6 = _.