Students learn to add two- and three-digit numbers using the standard algorithm, with a focus on regrouping (carrying). They begin with base-10 block models to see why 10 ones become 1 ten, then transition to the written vertical method. Problems progress from two-digit plus two-digit with one regrouping to three-digit problems with multiple regroupings.
K-2 Foundations • K-2
When we add big numbers, we line them up by place value and add one column at a time, starting from the ones (the right side). Sometimes a column adds up to 10 or more, and we need to regroup (also called "carrying").
Add 45 + 32.
If a column adds to 10 or more, write the ones digit below the line, and carry the tens digit to the next column.
Add 47 + 36.
Answer: 83
Add 278 + 365.
Before you add, estimate to check if your answer makes sense. Round each number to the nearest ten (or hundred), then add.
Do not forget to add the carried digit! It is the most common mistake. After you write the carry number above the next column, make sure you include it when you add that column.
You can add the numbers in the opposite order. Addition works in any order! If 47 + 36 = 83, then 36 + 47 should also equal 83.
If you have 47 stickers and your friend gives you 36 more, how many do you have? Line them up and add: 47 + 36 = 83 stickers!
1. Add: 56 + 23
56 + 23 = 79. Ones: 6+3=9. Tens: 5+2=7. No regrouping needed.
2. Add: 68 + 27
68 + 27 = 95. Ones: 8+7=15, write 5 carry 1. Tens: 1+6+2=9.
3. Add: 345 + 278
345 + 278 = 623. Ones: 5+8=13, write 3 carry 1. Tens: 1+4+7=12, write 2 carry 1. Hundreds: 1+3+2=6.
4. Add: 199 + 1
199 + 1 = 200. Ones: 9+1=10, write 0 carry 1. Tens: 1+9=10, write 0 carry 1. Hundreds: 1+1=2.
5. Estimate 287 + 415 by rounding to the nearest hundred, then find the exact answer.
Estimate: 300 + 400 = 700. Exact: 287 + 415 = 702. The estimate was very close!