Students explore how two-digit numbers are built from groups of ten and leftover ones using base-10 blocks and place value charts. They learn to decompose numbers like 47 into 4 tens and 7 ones, read and write two-digit numbers in expanded form, and understand that the position of a digit determines its value.
K-2 Foundations • K-2
Every number has a special place for each digit. When we write a two-digit number like 34, each digit tells us something different. The 3 tells us how many groups of ten we have. The 4 tells us how many ones are left over.
We group things by ten because it makes counting easier. Instead of counting 34 things one by one, we can make 3 groups of ten and have 4 left over.
We use special blocks to show numbers:
| Block | What It Looks Like | Value |
|---|---|---|
| Ones cube | A tiny single cube | 1 |
| Tens rod | A long stick made of 10 cubes | 10 |
To show the number 27, we use:
A place value chart has two columns for two-digit numbers:
| Tens | Ones |
|---|---|
| 2 | 7 |
Read this as: 2 tens and 7 ones, which equals twenty-seven.
Show 53 using base-10 blocks and a place value chart.
| Tens | Ones |
|---|---|
| 5 | 3 |
Expanded form shows a number as the sum of the value of each digit:
Write 95 in expanded form.
You have 6 tens rods and 2 ones cubes. What number is this?
Do not mix up tens and ones! In the number 38, the 3 does not mean three -- it means thirty (3 groups of ten). The 8 means eight ones.
Think of egg cartons that hold 10 eggs each. If you have 4 full cartons and 7 extra eggs, you have 47 eggs total!
1. How many tens and ones are in the number 74?
7 tens and 4 ones. The value of the tens digit is 70, and the value of the ones digit is 4.
2. Write 58 in expanded form.
58 = 50 + 8
3. You have 3 tens rods and 9 ones cubes. What number do you have?
39. Three tens is 30, plus 9 ones is 39.
4. What is the value of the digit 6 in the number 63?
60. The 6 is in the tens place, so it stands for 6 tens, which is 60.
5. A number has 0 tens and 5 ones. What is the number?
5. When there are 0 tens, the number is just the ones digit.