Subtract three-digit numbers by subtracting ones from ones, tens from tens, and hundreds from hundreds independently, without borrowing. This works when each digit in the minuend is greater than or equal to the digit below it.
Use base-ten blocks to model subtraction in each place value separately. Problems like 456 - 234 show the process clearly without needing to regroup.
You already know how to subtract numbers within 100 — subtracting ones from ones and tens from tens, each place value independently. Three-digit subtraction without regrouping extends that same idea by one more place: now you also subtract hundreds from hundreds. If you understood why 75 − 23 = 52 (5 ones minus 3 ones = 2 ones; 7 tens minus 2 tens = 5 tens), you already understand the logic of 475 − 223 = 252.
Place value is the organizing principle. When you write 456 − 234 in columns, you are really writing three separate subtraction problems stacked on top of each other: 6 − 4 in the ones column, 5 − 3 in the tens column, and 4 − 2 in the hundreds column. Each column produces one digit of the answer, and the columns do not interfere with each other — as long as every digit in the top number is greater than or equal to the digit below it in the same column. That condition is what "without regrouping" means.
To know whether a problem requires regrouping, look at each column from right to left before you start. In 456 − 234: ones column has 6 ≥ 4 (fine), tens column has 5 ≥ 3 (fine), hundreds column has 4 ≥ 2 (fine). All columns are safe, so you can subtract straight down. If you saw 456 − 278 instead, the ones column would have 6 ≥ 8? No — that signals regrouping is needed. For now, every problem you practice has been set up so that check always passes.
This topic is building toward the harder skill of three-digit subtraction with regrouping (borrowing), where a column does not have enough to subtract from. That skill is more complex, but it uses the same column structure. Getting comfortable with the no-regrouping version first means you know the framework before the exceptions are introduced. Think of these problems as the clean, predictable case that makes the messier case easier to understand when you reach it.