Column subtraction with regrouping

Quick answer

Learning outcome

• You can set up a subtraction problem in columns
• You can identify when you need to regroup (borrow)
• You can subtract correctly when regrouping is needed
• You can check your answer by adding it back to the number you subtracted from

Why this matters

How it works

1. Write the bigger number on top and the smaller number below, lining up the digits
2. Start from the right-hand column (units)
3. If the top digit is bigger than or equal to the bottom digit, subtract normally
4. If the top digit is smaller than the bottom digit, you must borrow from the next column to the left
5. When you borrow, take one from the next column and add ten to the current column
6. Continue working your way left through the columns

Examples you can see

1. Units column: 2 is less than 8, so we need to regroup
2. Take one from the tens column (5 becomes 4)
3. Add ten to the units column (2 becomes 12)
4. Now subtract: 12 - 8 = 4
5. Move to the tens column: 4 - 1 = 3
6. Answer: 34

1. Units column: 2 is less than 7, so we need to regroup
2. Take one from the tens column (0 becomes 9)
3. Add ten to the units column (2 becomes 12)
4. Subtract: 12 - 7 = 5
5. Tens column: 9 is greater than 5, so no regrouping needed
6. Subtract: 9 - 5 = 4
7. Hundreds column: 3 - 1 = 2
8. Answer: 145

Try it as a mini adventure

1. Units: 2 < 7, so borrow from tens
2. 42 becomes 3(12) = 32, 12 - 7 = 5
3. Tens: 3 - 1 = 2
4. Answer: 25

1. Units: 1 < 8, so borrow from tens
2. 701 becomes 7(10)1 = 701, 11 - 8 = 3
3. Tens: 0 < 4, so borrow from hundreds
4. 701 becomes (6)101 = 701, 10 - 4 = 6
5. Hundreds: 6 - 2 = 4
6. Answer: 453

1. Work backwards: 300 - 146 = ?
2. Units: 0 < 6, so borrow from tens
3. 300 becomes 2(10)0 = 300, 10 - 6 = 4
4. Tens: 9 < 4, so borrow from hundreds
5. 300 becomes (2)100 = 300, 10 - 4 = 6
6. Hundreds: 2 - 1 = 1
7. Answer: 154

Common mistakes

• Mistake: Forgetting to subtract one from the next column when borrowing
  Why it happens: Children may forget that borrowing means the next column goes down by one
  Fix: Always make a small mark or check that you've reduced the next column by one
• Mistake: Adding ten to the wrong column when regrouping
  Why it happens: Children may add ten to the column they're subtracting from instead of the one they're borrowing from
  Fix: Practice with visual aids like base-10 blocks or counters to see which column is which
• Mistake: Not checking the answer with addition
  Why it happens: Children may rush through and not double-check their work
  Fix: Always add your answer back to the number you subtracted from to see if you get the original number
• Mistake: Subtracting the smaller number from the larger number regardless of position
  Why it happens: Confusion about which number is the minuend and which is the subtrahend
  Fix: Always make sure the larger number is on top

Parent and carer guide

• Start with simple examples like 23 - 15
• Use base-10 blocks or counters to show regrouping
• Encourage your child to write down each step clearly
• Check their work by adding the answer back to the number they subtracted
• Practice with real-world examples like counting change or comparing scores
• Be patient if they make mistakes - this is normal learning
• Use games like "Subtraction Race" where you each write a subtraction problem and race to solve it
• Don't focus on speed, focus on understanding
• Ask your child to explain their thinking to you

Practice questions

1. 74 - 28 = ?
2. 82 - 37 = ?
3. 103 - 46 = ?
4. 502 - 278 = ?
5. 900 - 345 = ?

1. 46
2. 45
3. 57
4. 224
5. 555

FAQ

What is regrouping in subtraction?

Regrouping in subtraction means borrowing from the next column to the left when the top digit is smaller than the bottom digit. This allows you to complete the subtraction.

When do I need to regroup?

You need to regroup when the top digit in any column is smaller than the bottom digit. For example, if you're subtracting 7 from 2 in the units column, you must borrow from the tens column.

How do I know if my answer is correct?

You can check your answer by adding it back to the number you subtracted from. If you get the original number, your answer is correct.

Can I always regroup?

No, you only regroup when the top digit is smaller than the bottom digit. If it's larger or equal, you can subtract normally.

What happens if I have to regroup twice?

If you need to regroup twice, you borrow from the next column each time. For example, in 1000 - 345, you would borrow from the hundreds column to the tens column, then from the tens column to the units column.