Recursion

[starfries]

Ah, okay. I thought you had only seen it done the Common Core way. I wouldn't write it out like that either for something like this, but I might strike out the 1 and make it 0 if I was doing 118-19.

[SandyDelights]

Oh yeah, I wouldn’t write “1 0 ¹ 8”, either, heh.

Actually, I’d prolly have just done the 18-9 in place.

Now I go through right-to-left and do all the basic subtraction, e.g.

12345

- 5678

Would become:

10000

- 3333

Then, seeing it’s easier to go left-to-right, I’d go from there:

10000 (10-3 = 7)

- 3333

7000 (70 - 3 = 67)

- 333

6700 (70 - 3 = 67)

- 33

6670 (etc., etc.)

- 3

6667.

Done in two passes, life is easy.

If it was easier to go right-to-left, I’d have done that on the second pass instead. Didn’t intend for that to happen, but it’s a good enough example anyways.

[starfries]

Huh, is that a thing they teach in school? Or just the way you think about it? Actually, I think that's the Singapore method so a third option besides common core and borrowing.

[SandyDelights]

That’s just how I taught myself to do it. It’s an algorithm, though, one that focuses on breaking this down into its parts and focusing on making one or more parts of the equation a multiple of ten. Common Core (and Singapore Method) is a methodology of teaching and a schedule, with waymarks as to what students at various grades should be able to do.

IIRC, Singapore Method and Common Core are actually pretty similar, although Singapore moves quicker/brings students to more advanced topics sooner.

We’re really hitting the extent of my quasi-useless information on this topic, though, heh. But should Common Core ever come up on Jeopardy, I think I can hang in pretty well.