The left-to-right algorithm for subtracting multi-digit numbers feels highly unusual to most people when they learn it for the first time (especially to adults). This packet demonstrates the algorithm, and it suggests that there are some important connections between this algorithm and the ways people think about numbers.
This video demonstrates the basic algorithm and demonstrates its relationship to (1) the standard algorithm for subtracting multi-digit numbers, and (2) ways of thinking about subtracting multi-digit numbers.
This video demonstrates what happens when we need to regroup in the left-to-right algorithm.
This video demonstrates multiple regroupings.