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
,w_800.png)
Step 1
- 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
- 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
- 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