Students extend place value understanding to three-digit numbers by discovering the hundreds place. Using base-10 blocks, they see that 10 tens make 1 hundred, compose and decompose numbers like 365 into 3 hundreds, 6 tens, and 5 ones, and practice regrouping — trading 10 ones for 1 ten or 10 tens for 1 hundred.
K-2 Foundations • K-2
You already know about tens and ones. Now we go bigger! When we collect 10 tens, we can trade them for 1 hundred. This lets us write three-digit numbers like 365.
Our number system is built on groups of ten: 10 ones make 1 ten, and 10 tens make 1 hundred. This pattern goes on forever!
Three-digit numbers have three places:
| Hundreds | Tens | Ones |
|---|---|---|
| 3 | 6 | 5 |
The base-10 blocks for hundreds look like a flat square made of 100 tiny cubes (10 rows of 10).
| Block | Shape | Value |
|---|---|---|
| Ones cube | Tiny cube | 1 |
| Tens rod | Long stick | 10 |
| Hundreds flat | Big square | 100 |
What number is shown by 2 hundreds flats, 4 tens rods, and 7 ones cubes?
Composing means putting parts together to make a number. Decomposing means breaking a number into parts.
Sometimes we need to trade smaller pieces for bigger ones (or bigger ones for smaller):
10 ones = 1 ten
10 tens = 1 hundred
We do this when adding!
1 ten = 10 ones
1 hundred = 10 tens
We do this when subtracting!
You have 3 hundreds, 2 tens, and 15 ones. Regroup to write the correct number.
Each place can only hold one digit (0 through 9). If you count 12 tens, you must trade 10 of them for 1 hundred. 12 tens = 1 hundred and 2 tens.
Think about dollars, dimes, and pennies. 10 pennies = 1 dime. 10 dimes = 1 dollar. A dollar is like a hundred, a dime is like a ten, and a penny is like a one!
1. Write 473 in expanded form.
473 = 400 + 70 + 3
2. What number has 6 hundreds, 0 tens, and 9 ones?
609. When there are 0 tens, we write a 0 in the tens place.
3. You have 2 hundreds, 14 tens, and 3 ones. Regroup and write the number.
14 tens = 1 hundred + 4 tens. So 2+1 = 3 hundreds, 4 tens, 3 ones = 343.
4. How many tens are in the number 850?
The tens digit is 5, so there are 5 tens in the tens place. But the total number of tens in 850 is 85 (since 850 divided by 10 is 85).
5. Decompose 700 into hundreds, tens, and ones.
700 = 7 hundreds + 0 tens + 0 ones. In expanded form: 700 + 0 + 0.