Multi-Digit Addition & Subtraction

Grade 3 Mathematics

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Date:

The Big Idea

When we add or subtract big numbers, we work with one place value at a time.

Sometimes we need to regroup (trade 10 ones for 1 ten, or 10 tens for 1 hundred).

Remember: 10 ones = 1 ten | 10 tens = 1 hundred | 10 hundreds = 1 thousand

Example: Addition with Regrouping

Solve: 456 + 278

1 1
  456
+ 278
  734
  1. Ones: 6 + 8 = 14. Write 4, regroup 1 ten.
  2. Tens: 1 + 5 + 7 = 13. Write 3, regroup 1 hundred.
  3. Hundreds: 1 + 4 + 2 = 7. Write 7.
  4. Check: Estimate: 450 + 280 = 730. Our answer 734 is close!

Example: Subtraction with Regrouping

Solve: 542 - 178

4 13 12
  5̶4̶2
- 178
  364
  1. Ones: Can I take 8 from 2? NO! Regroup: 4 tens becomes 3 tens, and 2 ones becomes 12 ones. 12 - 8 = 4.
  2. Tens: Can I take 7 from 3? NO! Regroup: 5 hundreds becomes 4 hundreds, and 3 tens becomes 13 tens. 13 - 7 = 6.
  3. Hundreds: 4 - 1 = 3.
  4. Check: 364 + 178 = 542 ✓

Steps for Adding & Subtracting

  1. Estimate first! Round to the nearest 10 or 100 to predict your answer.
  2. Line up the digits by place value (ones under ones, tens under tens).
  3. Start with the ones place (on the right).
  4. For addition: If the sum is 10 or more, regroup.
  5. For subtraction: Ask "Can I?" before each step. If not, regroup.
  6. Check your answer! Compare to your estimate. Is it reasonable?

Always Check Your Work!

For addition: Does my answer match my estimate?

For subtraction: Add your answer + the number you subtracted. You should get the number you started with!

Example: 542 - 178 = 364. Check: 364 + 178 = 542 ✓

Your Turn: Addition

1. Solve 347 + 285. Show your work.

Estimate first: ______ + ______ = ______

Answer:

2. Solve 1,456 + 867. Show your work.

Estimate first: ______ + ______ = ______

Answer:

Your Turn: Subtraction

3. Solve 623 - 258. Show your work.

Estimate first: ______ - ______ = ______

Answer:

Check: ______ + 258 = ______

4. Solve 800 - 347. Show your work. (Watch out for the zeros!)

Estimate first: ______ - ______ = ______

Answer:

Check: ______ + 347 = ______

Your Turn: Word Problem

5. Maria read 486 pages last month and 597 pages this month. How many pages did she read in total?

What operation do I need? (circle one): Addition     Subtraction

Answer: pages

FAST Success Kit | Grade 3 | FL B.E.S.T. Standard: MA.3.NSO.2.1