I'm sorry I was not clear enough in my original question. My 2 dd remember how to subtract single or double digit numbers; their difficulty was w/ the 4 digit numbers.

I know we've done things w/ side 2 of the abacus, but none of those are in the games book.

Any more ideas? Or maybe just what lesson(s) in C or D to go to for directions on subtracting w/ side 2 of the abacus since we have those books as well?

Thanks for your help!

I'm not sure about D, but the lesson C sections you'll be looking for are lessons 90-94....hope that helps.

Book D, it looks like it's going to be around Lesson 44. But we're not there yet, so I'm not sure that's right (I don't have the book in front of me, I'm looking at the TofC online).

Thanks!