A student who recently came into our district from Australia shared this method of subtraction with me this morning when I was working with her in class. It was new to me, but it works. Unfortunately she was unable to explain the “why” behind it, which is what made me question it at first.
What I’m wondering is how my readers approach student-created algorithms in class. What is your criteria for accepting student-created algorithms? Do you encourage the use of alternative algorithms?
UPDATE: Here is a site that addresses and shows the justification for the Austrian method of subtraction shown above: