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Grade 1 Math Unit 2

Intro to Place Value through Addition and Subtraction within 20

Unit description: This unit serves as a bridge from problem solving within 10 to work within 100 as students begin to solve addition and subtraction problems involving teen numbers. In unit 1, students were encouraged to move beyond the beginning strategy of counting all to the more efficient counting on. Now, they go beyond that level to decomposition and composition strategies, informally called make ten or take from ten. Students will work on the concept of addition and subtraction within 20 and focus on building fluency within 10. Mastery of facts is not expected at this point in the year. They will develop an understanding of ten as a unit to analyze teens as ten and some ones and use modalities to build individual numbers with tens/ones while counting. Students will compare two two-digit numbers using symbols (<,>,=).

Essential Outcomes of the Unit

Numbers in Base Ten

Understand place value
  • 1.NBT.2 Understand that the two digits of a two-digit number represent amounts of tens and ones.
  • 1.NBT.2a Understand 10 can be thought of as a bundle of ten ones, called a “ten”.
  • 1.NBT.2b Understand the numbers from 11 to 19 are composed of a ten and one, two, three, four, five, six, seven, eight, or nine ones.
  • 1.NBT.3 Compare two two-digit numbers based on meanings of the tens and ones digits, recording the results of comparisons with the symbols >, =, and <.

Other Standards Addressed in this Unit

Operations in Algebraic Thinking

Represent and solve problems involving addition and subtraction.
  • 1.OA.1 Use addition and subtraction within 20 to solve one-step word problems involving situations of adding to, taking from, putting together, taking apart, and/or comparing, with unknowns in all positions.
    • Note: Problems should be represented using objects, drawings, and equations with a symbol for the unknown number. Problems should be solved using objects or drawings, and equations.
  • 1.OA.2 Solve word problems that call for addition of three whole numbers whose sum is less than or equal to 20.
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.
    • (Note: Students need not use formal terms for these properties. When students use the making ten strategy (NY-1.OA.6), they are applying the Associative property of addition.
  • 1.OA.4 Understand subtraction as an unknown-addend problem within 20.

All work with properties (NY-1.OA.3) and place value (e.g., NY-1.NBT.2 & 4) should be seen as an investigation and use of the structure of the number system and of arithmetic.

Add and subtract within 20.
  • 1.OA.5 Relate counting to addition and subtraction.
  • 1.OA.7 Understand the meaning of the equal sign, and determine if equations involving addition and subtraction are true or false. e.g., 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 with the unknown in all positions. e.g., Determine the unknown number that makes the equation true in each of the equations
    8 + ? = 11   – 3 = 5   6 + 6 = □

Essential Questions and Big Ideas

1. Why is it important to know multiple strategies in solving addition/subtraction problems?

    • Strategies can be used to decompose complex problems to make an easier problem.
    • Strategies help to solve addition and subtraction problems within 20 quicker.

2. How are problem solving strategies connected to number relationships?

    • Problem solving structures reinforce part/part/whole and number combinations within 20.
    • Each type of word problem situation (adding to, taking from, putting together, taking apart, comparing) reflects number relationships.

3. What is significant about the teen numbers (related to 10)?

    • Explain the value of each digit in a two digit number.
    • Represent a 2 digit numeral using “tens” and “ones.”
    • Build and decompose numbers into tens and ones.
    • Identify a bundle of 10 ones as a “ten”.

4. How is counting connected to quantity in a number?

    • Use comparison words greater than, less than, and equal to communicate understanding of the relationship between the numbers.

5. How does using objects and drawings help me represent problems in multiple ways?

    • Use models to represent 2 sets of numbers.
    • When given a set of objects (ranging from 0-120), represent the quantity with a written numeral.
    • Represent a problem situation involving 2-digit numbers using any combination of words, numbers, physical objects, or symbols.

Download the complete Grade 1 Math Unit 2 framework to customize for your own planning.