Concept 7 of 9
3-Digit Addition & Subtraction
Today's big idea
Three digits work the same way, one more column.
245 + 132: ones, tens, hundreds → 377.
How it works
👀 What's going on?
245 + 132: the same method, just one more column.
💡 Here's the trick
Three-digit sums work the same way. Line up hundreds, tens and ones, then go column by column.
245 + 132: ones 5 + 2 = 7, tens 4 + 3 = 7, hundreds 2 + 1 = 3. The answer is 377.
✍️ Try it
468 − 135: ones 3, tens 3, hundreds 3. → 333.
⚠️ Watch out
Carry or borrow between columns just as you do with two digits.
Watch me solve one
Quanta solves it
“Watch how I think through one of these — then you try.”
THE PROBLEM
“Add 356 + 231.”
- 1
Ones, then tens
6 + 1 = 7, and 5 + 3 = 8.
- 2
Then the hundreds
3 + 2 = 5.
- 3
Answer ✓
356 + 231 = 587
Now you try one — same steps, different story 👇
See it in action
⚡ Time to play!
Work from the right: ones, then tens, then hundreds.
245 + 132
Quick check
✅ VERIFICATION
What is 324 + 253?
⚡ Finish the activity above first to answer.
Keep going!
Up next: Word Problems & Estimating
Clue words pick add or subtract; round to check.