Primary 2 maths · Operations · About 12 minutes
Written addition with three digits
Align hundreds, tens and ones and include carried units in three-digit addition
Start the interactive lesson →Practise: Addition architect
What you will learn
- Align hundreds, tens and ones and include carried units in three-digit addition
Models used: place-value charts, number sentences, bar models, stories.
Before you start
Give each place its own column
Work out 268 + 157.
Line up ones under ones and tens under tens. Start on the right.
268 + 157
hundreds tens ones Carried units First number 2 6 8 + 1 5 7 Answer ? ? ? 15 ones make 1 ten and 5 ones. Write 5 here. Carry 1 to the next column.
8 + 7 = 15
hundreds tens ones Carried units 1 First number 2 6 8 + 1 5 7 Answer ? ? 5 1 ten⇄10 ones
12 tens make 1 hundred and 2 tens. Write 2 here. Carry 1 to the next column.
6 + 5 + 1 = 12
hundreds tens ones Carried units 1 1 First number 2 6 8 + 1 5 7 Answer ? 2 5 1 hundred⇄10 tens
Add the hundreds, including the carried 1. Write 4 in this column.
2 + 1 + 1 = 4
hundreds tens ones Carried units 1 1 First number 2 6 8 + 1 5 7 Answer 4 2 5 Read the answer from left to right. Subtract one addend to check.
425 − 157 = 268
hundreds tens ones Carried units 1 1 First number 2 6 8 + 1 5 7 Answer 4 2 5
Worked example: Fill one answer box at a time
Work out 356 + 278.
| hundreds | tens | ones | |
|---|---|---|---|
| Carried units | |||
| First number | 3 | 5 | 6 |
| + | 2 | 7 | 8 |
| Answer | ? | ? | ? |
Line up ones under ones and tens under tens. Start on the right.
356 + 278
hundreds tens ones Carried units First number 3 5 6 + 2 7 8 Answer ? ? ? Make the exchange. Then fill the highlighted answer box.
hundreds tens ones Carried units 1 First number 3 5 6 + 2 7 8 Answer ? ? ? 1 ten⇄10 ones
What digit do we write in the ones column?
4
Make the exchange. Then fill the highlighted answer box.
hundreds tens ones Carried units 1 1 First number 3 5 6 + 2 7 8 Answer ? ? 4 1 hundred⇄10 tens
What digit do we write in the tens column?
3
Work in the highlighted column.
hundreds tens ones Carried units 1 1 First number 3 5 6 + 2 7 8 Answer ? 3 4 What digit belongs in the hundreds column?
6
Read the answer from left to right. Subtract one addend to check.
634 − 278 = 356
hundreds tens ones Carried units 1 1 First number 3 5 6 + 2 7 8 Answer 6 3 4
Common mistakes to discuss
- Forget a carried unit. Include the small carried digit above the next column.
- Write two digits in one box. Keep one digit in each answer column; exchange ten units for one next-place unit.
Check your understanding
- Line up matching places.
- Exchange ten ones for a ten and include every carried unit.
- Check the total with subtraction.
Explain your reasoning to an adult, then try a fresh question in the interactive lesson. A result from one attempt is not proof of lasting mastery.
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