Method F - Constant Difference Method
CPD: A Compendium of Mathematical Methods (By Jo Morgan), topic 2.1.6
Constant Difference Theory: 753 − 491
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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.
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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