Source: https://senecalearning.com/en-gb/revision-notes/teacher-cpd/cpd-for-primary-subtraction-methods-for-ks2-maths-seneca-certified/2-1-6-method-f-constant-difference-method

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# Method F - Constant Difference Method

CPD for Primary: Subtraction Methods for KS2 Maths (by Jo Morgan), topic 2.1.6

## Constant Difference Theory: 753 − 491

### Step 1

![Step 1](https://image-v2.cdn.app.senecalearning.com/2020-04/95b12ffa-0e55-4de9-948e-5004323faa4d/Method%20F%20-%20Example%201%20(1).png)

- We are trying to avoid any carrying or exchanging – the problem is the middle digit in the subtrahend being a 9. 
- So we could add 10 to both the minuend and the subtrahend to make the subtraction easier.

### Step 2

![Step 2](https://image-v2.cdn.app.senecalearning.com/2020-05/ad800cd2-37be-4655-ba36-1a7efbeef9c5/Method%20F%20-%20Example%201.png)

- We write out the new subtraction in the usual column format. 
- This isn’t totally necessary though because we just need to subtract the hundreds from the hundreds, the tens from the tens and the ones from the ones. 
- We can work left to right or right to left (because no exchanges are required), with or without the column format.

### Answer

![Answer](https://image-v2.cdn.app.senecalearning.com/2020-05/38202c8d-a7e5-4d44-815a-224478530d09/Method%20F%20-%20Example%202.png)

- So if 763 − 501 = 262, then 753 − 491 = 262.

## Test yourself on Method F - Constant Difference Method

- What is the Constant Difference Method also known as?
- What should students add or subtract from the minuend and subtrahend in this calculation to make it simpler?5500 − 4174

[Practise this topic for free](https://app.senecalearning.com/classroom/course/eab4f483-2118-4224-8daa-b5f64232f209/section/8aaeb466-d484-4ce6-b0ff-f045795cd700/session)

- Previous topic: [2.1.5 Method E - Counting-Up Method](https://senecalearning.com/en-gb/revision-notes/teacher-cpd/cpd-for-primary-subtraction-methods-for-ks2-maths-seneca-certified/2-1-5-method-e-counting-up-method.md)
- Next topic: [2.1.7 Method G - Partial Differences Method](https://senecalearning.com/en-gb/revision-notes/teacher-cpd/cpd-for-primary-subtraction-methods-for-ks2-maths-seneca-certified/2-1-7-method-g-partial-differences-method.md)

## CPD for Primary: Subtraction Methods for KS2 Maths (by Jo Morgan) contents

### 1 Course Overview
- 1.1 Course Structure & Commonly Asked Questions
  - [1.1.1 Introduction to the Course & Common Questions](https://senecalearning.com/en-gb/revision-notes/teacher-cpd/cpd-for-primary-subtraction-methods-for-ks2-maths-seneca-certified/1-1-1-introduction-to-the-course-and-common-questions.md)

### 2 Subtraction Methods
- 2.1 Subtraction Methods
  - [2.1.1 Method A - Decomposition Method](https://senecalearning.com/en-gb/revision-notes/teacher-cpd/cpd-for-primary-subtraction-methods-for-ks2-maths-seneca-certified/2-1-1-method-a-decomposition-method.md)
  - [2.1.2 Method B - Equal Addition Method](https://senecalearning.com/en-gb/revision-notes/teacher-cpd/cpd-for-primary-subtraction-methods-for-ks2-maths-seneca-certified/2-1-2-method-b-equal-addition-method.md)
  - [2.1.3 Method C - Expanded Form Method](https://senecalearning.com/en-gb/revision-notes/teacher-cpd/cpd-for-primary-subtraction-methods-for-ks2-maths-seneca-certified/2-1-3-method-c-expanded-form-method.md)
  - [2.1.4 Method D - Partitioning Method](https://senecalearning.com/en-gb/revision-notes/teacher-cpd/cpd-for-primary-subtraction-methods-for-ks2-maths-seneca-certified/2-1-4-method-d-partitioning-method.md)
  - [2.1.5 Method E - Counting-Up Method](https://senecalearning.com/en-gb/revision-notes/teacher-cpd/cpd-for-primary-subtraction-methods-for-ks2-maths-seneca-certified/2-1-5-method-e-counting-up-method.md)
  - [2.1.6 Method F - Constant Difference Method](https://senecalearning.com/en-gb/revision-notes/teacher-cpd/cpd-for-primary-subtraction-methods-for-ks2-maths-seneca-certified/2-1-6-method-f-constant-difference-method.md)
  - [2.1.7 Method G - Partial Differences Method](https://senecalearning.com/en-gb/revision-notes/teacher-cpd/cpd-for-primary-subtraction-methods-for-ks2-maths-seneca-certified/2-1-7-method-g-partial-differences-method.md)
  - [2.1.8 Method H - Complementary Method](https://senecalearning.com/en-gb/revision-notes/teacher-cpd/cpd-for-primary-subtraction-methods-for-ks2-maths-seneca-certified/2-1-8-method-h-complementary-method.md)
  - [2.1.9 Method I - Nines Complement Method](https://senecalearning.com/en-gb/revision-notes/teacher-cpd/cpd-for-primary-subtraction-methods-for-ks2-maths-seneca-certified/2-1-9-method-i-nines-complement-method.md)