The point was usually to illustrate a variety of different mental motions that a young mathematician might be making, OTHER than the one intended by the algorithm. So all sorts of examples are possible, and there were a number of things found in clinical interviews. Not just instances of one single pattern.
Don’t leave us hanging… Could you please provide one or two more examples?
34-16=12?
63-17=11?
The point was usually to illustrate a variety of different mental motions that a young mathematician might be making, OTHER than the one intended by the algorithm. So all sorts of examples are possible, and there were a number of things found in clinical interviews. Not just instances of one single pattern.
34–16 yields 13
63–17 yields 16
For the four examples of
24-16=12, 53-25=25, 34-16=13, 63-17=16
is this the pattern?
ab-cd=ca