# 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.