so what if one doesn’t use 20, 3 and 4?
I’m no big fan of Common Core but the chart is interesting. The old way is the best for mechanically cranking out the answer to the problem.
It is the right way to teach arithmetic to children.
The second solution is simply a way of doing iit in your head. It’s not the best way but it works. The best way to do it in your head:
54-30 = 24 and add 30-27 which equals 3 to get 27. That’s actually the way most people would do it in their head.
However, it is a stupid way to do it on paper. And is certainly not the way to teach arithmetic.
The “new way” will be good for educating cashiers to give change... sadly those jobs have been outsourced to self-checkout lines.