New
New
Year 5

# Use knowledge of column addition and subtraction to calculate with decimal numbers

I can use knowledge of column addition and subtraction to calculate with decimal numbers.

New
New
Year 5

# Use knowledge of column addition and subtraction to calculate with decimal numbers

I can use knowledge of column addition and subtraction to calculate with decimal numbers.

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## Lesson details

### Key learning points

1. Numbers are recorded in columns with the same value digits in each column.
2. Start with the smallest value column in case numbers need to be regrouped or exchanged.
3. If the value of a digit in the minuend is greater than the same digit in the subtrahend, you will need to exchange.
4. Make sure that any regrouped numbers are added in with others of the same value.

### Common misconception

Pupils regroup incorrectly, particularly when subtracting e.g. exchanging one ten for ten ones.

Build the calculation using place value counters on a grid set out like a column method. Ask pupils to represent regrouping with counters.

### Keywords

• Decimal number - A decimal number has a decimal point followed by digits that show the fractional part.

• Regrouping - The process of unitising and exchanging between place values is known as regrouping. For example: ten ones can be regrouped for one ten.

• Place value - The value of a digit in a number based on where it is placed.

For worded problems, ask pupils to represent the problem as a bar model at first. This will help them to identify whether the wholes or parts are missing and whether they need to add or subtract.
Teacher tip

### Licence

This content is Â© Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

## Starter quiz

### 6 Questions

Q1.
Tick all the expressions that would make or bridge 10.
4 + 5
2 + 7
Q2.
Order the expressions from the smallest amount to the largest amount.
1 - 3 + 2
2 - 11 - 5
3 - 5 + 3
4 - 14 - 5
5 - 6 + 7
6 - 9 + 5
Q3.
Q4.
Complete the column subtraction and write in the answer.
Q5.
Tick the calculations that require a regrouping.
Correct Answer: An image in a quiz
Correct Answer: An image in a quiz
Q6.
Tick the correct explanation of the mistake that has been made.
They have regrouped too many tens.
They did not need to regroup.
Correct answer: They have forgotten to reduce the tens to 6 tens when they regrouped.

## Exit quiz

### 6 Questions

Q1.
Tick the explanation that explains why the column addition is laid out incorrectly.
Correct answer: There are too many digits in one column.
The decimal points are not lined up correctly.
Although adding decimals, there is no decimal point within the sum.
Q2.
271.1
27.1
27.11
Q3.
Complete the column subtraction and write in the correct answer.