Addition & Subtraction – Grade 3 Maths

Mental Bridging

Adding through a round number like 100 or 200

Column Addition

3-digit addition with carrying

Column Subtraction

3-digit subtraction with borrowing

Estimating

Using rounding to check your answer

Inverse Operations

Using addition to check subtraction

Word Problems

Solving real-life addition and subtraction

1. Mental Bridging

Bridging means jumping through a round number to make addition easier.

To add 47 + 56: bridge through 100!
47 + 53 = 100, then add 3 more → 103

Add 364 + 136:
Step 1: 364 + 36 = 400 (bridge to 400)
Step 2: 400 + 100 = 500
Answer: 500

🍰 Split the number you're adding so the first part fills up to a round number — like filling a cupcake tray exactly!

2. Column Addition (with carrying)

Line up digits by place value: hundreds, tens, ones. Add from right to left.

          2 3 8

        + 2 1 9

        ───────

        Ones: 8+9=17 → write 7, carry 1

        Tens: 3+1+1=5 → write 5

        Hundreds: 2+2=4 → write 4

        = 457

🍬 Always start with the ones column! If the total is 10 or more, carry the 1 to the next column.

3. Column Subtraction (with borrowing)

Line up digits and subtract from right to left. If a digit is too small, borrow from the column to the left.

          5 4 3

        − 3 3 0

        ───────

        Ones: 3−0=3

        Tens: 4−3=1

        Hundreds: 5−3=2

        = 213

        Borrowing example:

          4 2 3

        − 0 8 1

        ───────

        Ones: 3−1=2

        Tens: 2<8, borrow! 12−8=4, hundreds become 3

        Hundreds: 3−0=3

        = 342

🍩 When a digit is too small to subtract, borrow 1 from the column on the left — it becomes 10 extra in your current column!

4. Estimating

Round each number to the nearest 100 first to get a rough answer, then check with the exact calculation.

Estimate 358 + 124:
Round: 400 + 100 = 500
Exact: 358 + 124 = 482
482 is close to 500, so the answer is reasonable!

🌈 Estimating is like a sense-check — it helps you spot mistakes before they become problems!

5. Inverse Operations

Addition and subtraction are opposites. You can use one to check the other.

If A + B = C, then C − B = A and C − A = B

Check: 357 + 125 = 482
Use inverse: 482 − 125 = 357 ✓

Check: 500 − 213 = 287
Use inverse: 287 + 213 = 500 ✓

🍭 Always check your subtraction by adding back — if you get the starting number, you're right!

6. Word Problems

Read carefully, find the key numbers and decide: add or subtract?

Key words for addition: total, altogether, more, sum, plus, in all

Key words for subtraction: difference, less, fewer, left, how many more, take away

A bakery has 247 doughnuts. They make 336 more.
How many doughnuts altogether?
247 + 336 = 583

🎂 Underline the key words and numbers — they tell you exactly what to do!

Example 1 — Column Addition

Calculate 238 + 219.

Ones: 8 + 9 = 17 → write 7, carry 1

Tens: 3 + 1 + 1(carry) = 5

Hundreds: 2 + 2 = 4

Answer: 457

Example 2 — Column Subtraction

Calculate 543 − 330.

Ones: 3 − 0 = 3

Tens: 4 − 3 = 1

Hundreds: 5 − 3 = 2

Answer: 213

Example 3 — Bridge Through 100

Calculate 364 + 136 mentally.

How much to next hundred? 364 + 36 = 400

Remaining: 136 − 36 = 100. Add that: 400 + 100 = 500

Example 4 — Missing Number

? + 184 = 430. What is the missing number?

Use the inverse: 430 − 184 = ?

430 − 184 = 246

Example 5 — Word Problem

A sweet shop has 338 lollipops and 245 gummies. How many sweets altogether?

Key word: "altogether" → add

338 + 245 = 583

🎯 Step-by-Step Column Calculator

First number: Second number:

Click Calculate to see step-by-step working!

Exercise 1 — Column Addition

1. 238 + 219 = ?

2. 314 + 321 = ?

3. 456 + 358 = ?

4. 467 + 455 = ?

5. 384 + 317 = ?

6. 274 + 289 = ?

7. 365 + 383 = ?

8. 446 + 445 = ?

9. 257 + 343 = ?

10. 572 + 428 = ?

Exercise 2 — Column Subtraction

1. 543 − 330 = ?

2. 678 − 336 = ?

3. 729 − 313 = ?

4. 835 − 253 = ?

5. 694 − 447 = ?

6. 423 − 258 = ?

7. 563 − 235 = ?

8. 742 − 251 = ?

9. 483 − 329 = ?

10. 615 − 306 = ?

Exercise 3 — Mental Addition (bridge through 100)

1. 364 + 106 = ?

2. 394 + 136 = ?

3. 452 + 148 = ?

4. 584 + 166 = ?

5. 647 + 173 = ?

6. 278 + 132 = ?

7. 393 + 167 = ?

8. 512 + 178 = ?

9. 663 + 177 = ?

10. 724 + 186 = ?

Exercise 4 — Find the Missing Number

1. ? + 184 = 430

2. 216 + ? = 354

3. ? + 253 = 680

4. 187 + ? = 502

5. ? + 341 = 850

6. 256 + ? = 429

7. ? + 162 = 446

8. 198 + ? = 594

9. ? + 267 = 728

10. 314 + ? = 841

Exercise 5 — Word Problems

1. A bakery bakes 247 doughnuts and 336 cookies. How many altogether?

2. There are 654 sweets. 187 are eaten. How many are left?

3. A shop has 385 red lollipops and 356 blue lollipops. How many in total?

4. Tom has 512 stickers. He gives 187 away. How many does he have left?

5. Year 3 raises £487. Year 4 raises £409. What is the total?

6. A jar holds 450 jelly beans. 236 are eaten. How many are left?

7. A cinema has 284 seats downstairs and 274 upstairs. Total seats?

8. A farmer has 642 apples and sells 239. How many remain?

9. Class A has 345 crayons and class B has 327. How many altogether?

10. A library has 538 books. 349 are borrowed. How many are still on the shelves?

🏋️ Practice — 20 Questions

1. 457 + 385 = ?

2. 384 + 287 = ?

3. 265 + 269 = ?

4. 536 + 387 = ?

5. 423 + 394 = ?

6. 678 − 333 = ?

7. 542 − 251 = ?

8. 437 − 146 = ?

9. 746 − 283 = ?

10. 854 − 154 = ?

11. 186 + 57 = ?

12. 374 − 187 = ?

13. 178 + 178 = ?

14. 546 − 127 = ?

15. 264 + 318 = ?

16. 715 − 87 = ?

17. ? + 162 = 269 (missing number)

18. 214 + 181 = ?

19. 389 + 355 = ?

20. 524 − 264 = ?

🏆 Challenge — 8 Questions

1. 238 + 138 = ?

2. 436 − 188 = ?

3. 572 + 428 = ?

4. 753 − 753 = ?

5. 345 + 342 = ?

6. 512 − 349 = ?

7. 456 + 443 = ?

8. 200 − 99 = ?

➕➖ Addition & Subtraction