So I’ve been trying to find out an alternate way to subtract, and talking with a co worker we have come across a method we both have used in the past, but neither of us can remember how we did it.
Growing up in the US, I’ve learned the traditional subtraction method by subtracting vertically, and working from left to right (ones place, tens place, hundreds, etc…)
However, I know that I have used a reverse method of starting at the opposite side and working right. My co worker had taught his daughter this method when the previous one was evading her in elementary 20 years ago.
It isn’t the Austrian method, and I can’t find anything online.
Could one of you fine, upstanding examples of the teeming millions be able to fight my recurring ignorance on this issue?
I don’t know about “a” method as such. I taught myself to add/subtract left to right in 2nd grade. You just use the “regular” method with look-ahead for carry/borrow.
(Reason for inventing this method: Contests at the blackboard. The teacher would read out two numbers. As the 2nd number is being read off, I was already starting to write down the answer. Won every time. Did not please the teacher of course.)
>I’ve learned the traditional subtraction method by subtracting vertically, and working from left to right (ones place, tens place, hundreds, etc…)
That IS right to left.
Subtracting while starting at the left or most significant column requires that you know the column relationship between the numbers. That is, to start calculating an answer while the second number is being read, you have to hear where the first columns you hear are.
It is better to work left to right if you don’t need an exact answer, which is often the case.