1) Can I take 7 from zero?
2) Can I borrow from a neighbor with nothing?
3) Can I borrow from two neighbors with nothing?
4) Can I borrow from 3 neighbors with 200?
Then I have them mark through the entire 200, borrow one from it leaving 199, then make my 0 in the one's place a ten. Subtract:
1 9 9 10
This is so much less complicated than borrow from the thousand's place, make it 1, now the hundred's place becomes ten, borrow from it, making it nine and making the ten's place......