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Addition & Subtraction

Adding and subtracting numbers within 1000, including regrouping across tens and hundreds.

Learn it step by step

Add ones first, then tens, then hundreds

To add $256 + 137$ , add the ones $6 + 7 = 13$ , then the tens, then the hundreds, carrying over any extra ten or hundred as you go.

Regrouping means carrying an extra 10

When the ones add up to 10 or more, regroup: 10 ones become 1 ten. In $256 + 137$ , $6 + 7 = 13$ , so write down $3$ and carry $1$ ten to the tens column.

13 ones is the same as 1 ten and 3 ones.

Subtraction may need borrowing

When the top digit is smaller than the bottom digit, borrow 1 ten (or 1 hundred) from the next place. In $423 - 156$ , the ones digit $3$ is smaller than $6$ , so borrow 1 ten from the tens place.

Check subtraction by adding back

After subtracting, add the answer to the number you subtracted; it should give back the original number. $423 - 156 = 267$ , and $267 + 156 = 423$ checks out.

Solve word problems by deciding add or subtract

Look for clue words: "altogether" or "in total" usually means add; "how many more", "how many left", or "difference" usually means subtract.

Look and learn

Work out 264 + 178.

Add the ones: $4 + 8 = 12$ , write 2, carry 1 ten.
Add the tens: $6 + 7 + 1 = 14$ , write 4, carry 1 hundred.
Add the hundreds: $2 + 1 + 1 = 4$ .
264 + 178 = 442.

Work out 502 - 268.

Ones: 2 is smaller than 8, so borrow 1 ten from the tens. 0 tens means borrow 1 hundred first, making it 4 hundreds, 10 tens, 2 ones.
Borrow 1 ten for the ones: 12 - 8 = 4; tens left: 9.
Tens: 9 - 6 = 3.
Hundreds: 4 - 2 = 2.
502 - 268 = 234.

A shop sold 348 apples on Monday and 275 apples on Tuesday. How many apples were sold altogether?

"Altogether" means add.
$348 + 275$ : ones $8 + 5 = 13$ , write 3 carry 1.
Tens: $4 + 7 + 1 = 12$ , write 2 carry 1. Hundreds: $3 + 2 + 1 = 6$ .
Total: 623 apples.

Ravi has 420 stamps. He gives away 165 stamps. How many stamps does he have left?

"Left" means subtract: $420 - 165$ .
Ones: 0 - 5, borrow: 10 - 5 = 5, tens become 1.
Tens: 1 - 6, borrow: 11 - 6 = 5, hundreds become 3.
Hundreds: 3 - 1 = 2.
Ravi has 255 stamps left.

Mind map

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