I’m beginning to realise why maths never made sense to me. I’ve just tried to explain the version of subtraction i have always used and i can’t. It doesn’t make sense. (And here’s where i have to own up to the fact that most of the links Alison left me the other night whirled above my head too.)
I was always taught like this
Okay you can’t take 8 from 2 so you borrow 10 from the bottom, the 2 becomes 12 and the 5 becomes a 6. Then it all works perfectly. And it does – only when i tried to explain that, with base 10, i can’t give her any reasonable explaination of what i’m doing. It doesn’t make sense. Why am i doing that?
So i look in the CGP book – IT says:
make the 2 into 12 but borrow from the 6 within the same number. This seems to make a certain amount more sense – the 2 becomes 12, the 6, having lost a 10, becomes a 5. So i think we can do it that way.
But why on earth was i ever taught the other way?