Adding 2- and 3-Digit Numbers
Adding 2- and 3-Digit Numbers
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Adding 2- and 3-Digit Numbers
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Learning goal
I can add 2-digit and 3-digit numbers accurately, with and without regrouping.
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One word or phrase you connect with column addition
Use this to surface prior knowledge such as place value, lining up digits, carrying, regrouping, tens, ones, or checking.
Place value helps us add
Digits have different values depending on their place.
In 47, the 4 means 4 tens and the 7 means 7 ones.
In 326, the 3 means 3 hundreds, the 2 means 2 tens, and the 6 means 6 ones.
When we add, we match ones with ones, tens with tens, and hundreds with hundreds.
Stress that addition works by combining equal place values. This prepares students for column addition and regrouping.
Line up the digits correctly
Write numbers in columns.
Ones go under ones.
Tens go under tens.
Hundreds go under hundreds.
Correct layout helps prevent mistakes.
Model a common error such as misaligning 56 and 203, then correct it by placing each digit in the proper column.
Adding without regrouping
If a column totals 9 or less, no regrouping is needed.
Example:
34 + 25
Ones: 4 + 5 = 9
Tens: 3 tens + 2 tens = 5 tens
Answer: 59
Use the phrase 'no regrouping' consistently. Emphasise that each column stays within one digit.
A 3-digit example
Example:
243 + 154
Ones: 3 + 4 = 7
Tens: 4 tens + 5 tens = 9 tens
Hundreds: 2 hundreds + 1 hundred = 3 hundreds
Answer: 397
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When adding 243 + 154, which digits should match?
Ones with ones
Ones with tens
Tens with hundreds
Hundreds with ones
Checks the key idea from the first block: equal place values must be added together.
Complete the place value idea
In column addition, we line up digits by place value. We add ones first, then tens, then hundreds. If a column totals 9 or less, there is no regrouping.
Echoes the wording from slides 2 to 5 without adding a new method.
What regrouping means
Regrouping happens when a column totals 10 or more.
10 ones = 1 ten
10 tens = 1 hundred
We write the extra value in the next column to keep the place values correct.
Some pupils may know this as 'carrying'. Use 'regrouping' as the main term, but note that both refer to the same idea.
Regrouping with 2-digit numbers
28 + 17
Ones: 8 + 7 = 15
Write 5 ones, regroup 1 ten
Tens: 2 + 1 + 1 regrouped = 4 tens
Answer: 45
Connect the regrouped ten to concrete imagery: 10 ones combine to make 1 ten.
Regrouping with 3-digit numbers
186 + 247
Ones: 6 + 7 = 13 → write 3, regroup 1 ten
Tens: 8 + 4 + 1 = 13 tens → write 3 tens, regroup 1 hundred
Hundreds: 1 + 2 + 1 = 4 hundreds
Answer: 433
This example shows regrouping in more than one column. Pause after each column so students can track the exchanged value.
Checking your addition
Check that the digits are lined up correctly.
Add from right to left: ones, tens, hundreds.
Make sure each regrouped value is added in the next column.
Ask: Does my answer look sensible?
You may mention estimation orally, for example checking that 186 + 247 should be a little over 400.
Common mistakes to avoid
Mixing up place value columns.
Forgetting to regroup when the total is 10 or more.
Regrouping, but not adding the extra 1 in the next column.
Starting with the hundreds instead of the ones.
These errors directly answer why students get inaccurate totals even when they know basic number facts.
When do we need to regroup?
When a column is 9
When a column is 10 or more
When you start with hundreds
When digits are equal
Targets the definition of regrouping from slide 6.
Complete the regrouping steps
In 28 + 17, the ones make 15. We write 5 ones and regroup 1 ten. In the next column, we must add the extra 1.
Checks that pupils track both writing the ones digit and adding the regrouped value in the next column.
What is one way to check your addition?
Look for one specific strategy from the lesson, such as line up digits, start with ones, check regrouping, or see if the answer looks sensible.
What helped you most in this lesson?
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Which part of addition still feels tricky?
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Glossary
addition - finding the total when numbers are combined
digit - a single number symbol from 0 to 9
place value - the value of a digit because of its position
ones - the first place value column
tens - the second place value column, worth groups of 10
hundreds - the third place value column, worth groups of 100
regrouping - moving 10 of one place value to make 1 of the next place value
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