1.NBT.B.2

Understand that the two digits of a two-digit number represent amounts of tens and ones. Understand the following as special cases:

-
10 can be thought of as a bundle of ten ones — called a “ten.”
  - The numbers from 11 to 19 are composed of a ten and one, two, three, four, five, six, seven, eight, or nine ones.
  - The numbers 10, 20, 30, 40, 50, 60, 70, 80, 90 refer to one, two, three, four, five, six, seven, eight, or nine tens (and 0 ones).

 

Summary:

The concept of tens and ones is the foundational basis for our numeric system; students should be exposed to the idea of bundling 10 ones immediately. Students must be familiar with and demonstrate their knowledge of this basic premise that a one-digit number indicates the number of ones, while a two-digit number indicates the number of tens and ones.  The idea that each digit in a two-digit number has a specific value is key to this standard. Students should be exposed to the idea of bundling 10 ones immediately. Often, this is referred to as making a trade.


Understanding the Standard:


    • Provide opportunities for students to work with decomposing two-digit numbers in order to see the value of each digit. For instance, 14 is decomposed as one ten (or one bundle of 10 ones) and 4 ones.
    • Provide students with opportunities to use manipulatives and technologies which allow students to physically make bundles of tens. This helps with moving an abstract concept into more concrete terms.
    • Provide students with problems/opportunities to think of the number 10 as ten ones and a ten, and of the numbers 11, ..., 19 as whole numbers after 10 (e.g., 11 ones) and as a ten and a certain number of ones (e.g., one ten and 1 one).
    • Provide students with problems/opportunities to think of and verbalize the numbers 10, 20, ..., 90 as a certain number of tens and zero ones.

    Specific Questions to focus Instruction:


      • Can students bundle a group of 10 ones into a ten and understand that 10 ones and a ten have the same value?
      • Do students understand that the two-digit numbers 11, 12, ..., 19 are composed of one ten and so many ones?
      • Do students understand that 11, ..., 19 can be thought of as whole numbers after ten and as a certain number of ones?
      • Can students verbalize the number of tens and ones that represent two-digit numbers (up to 20 and beyond)?
      • Do students understand that 10, 20, and so on refer to a certain number of tens and 0 ones?
      • Can students explain their reasoning?

        Skills

        Prior to: Students can read, count and recognize numbers through 10. Go to K.NBT.A.1 to see previous skills in this progression.


        At grade level:
        Students can represent numbers through 20, recognizing that two-digit numbers are composed of a certain number of tens and an appropriate number of ones. Students can recognize multiples of 10 as that many sets of tens (for example, 90 is 9 sets of tens).

        Moving Beyond:
        Students will build upon this skill and use their knowledge of bundling and making a trade in order to perform addition and subtraction where regrouping is necessary. From there, they will be introduced to the concept of bundling 10 tens as one hundred. Go to 2.NBT.A.1 to see the progression of related skills.

        This continuum contains Counting and Cardinality standards for K, Number and Operations and Algebraic Thinking standards K-3, Number and Operations in Base Ten standards K-3, Number and Operations – Fractions standards for grade 3.