Lesson 4.3 · Adding and Subtracting Within 1,000
Subtracting three-digit numbers
Subtracting three-digit numbers works just like subtracting two-digit numbers. Start with the ones. Then do the tens. Then do the hundreds.
Subtract each place
Find 587 − 243.
Ones: 7 − 3 = 4. Tens: 8 − 4 = 4. Hundreds: 5 − 2 = 3.
So 587 − 243 = 344.
When you need more
Sometimes the top digit is too small. Then you regroup.
- Break 1 ten into 10 ones.
- Break 1 hundred into 10 tens.
Subtracting three-digit numbers
Line up the places. Subtract the ones, then the tens, then the hundreds.
If the top digit is smaller, break 1 from the next place to the left into 10.
Worked example: 452 − 128
Ones: 2 − 8? Not enough ones. Break 1 ten into 10 ones. Now there are 12 ones and 4 tens.
12 − 8 = 4. Tens: 4 − 2 = 2. Hundreds: 4 − 1 = 3.
The answer is 324.
Worked example: 603 − 275
603 has 0 tens, so you can't break a ten yet. Break 1 hundred first.
603 = 5 hundreds, 10 tens, 3 ones. Now break 1 ten: 5 hundreds, 9 tens, 13 ones.
Ones: 13 − 5 = 8. Tens: 9 − 7 = 2. Hundreds: 5 − 2 = 3.
The answer is 328.
Worked example: Count up: 500 − 296
296 is very close to 300. Count up from 296 instead of taking away.
296 to 300 is 4. 300 to 500 is 200. 4 + 200 = 204.
So 500 − 296 = 204.
Tip
Check with addition. If 452 − 128 = 324, then 128 + 324 should be 452. It is!
Common mistake
Don't subtract the smaller digit from the bigger one just because it is easier. In 452 − 128, the ones are 2 − 8. You must regroup. Doing 8 − 2 gives the wrong answer, 336.
Practice
What is 768 − 345?
Type a number.
What is 594 − 172?
Type a number.
What is 641 − 326?
Type a number.
What is 725 − 381?
Type a number.
What is 832 − 457?
Type a number.
What is 500 − 168?
Type a number.
Liam says 614 − 239 = 425. What is the right answer?
A farm has 405 eggs. It sells 178 eggs. How many eggs are left?
Type a number.