Minus nine and add one.

Minus eight plus two.

Negative seven plus three.

Negative six plus four.

Minus five and add five.

Negative four plus six.

Negative three plus seven.

Minus two and add eight

12-9=2+ 1=3

17-8=7+2=9

1 1–7= 1+3=4

13-6=3+4=7

Ten-fold method: a calculation method

That is, when the number of units is not enough, subtract the subtraction with 10 and add the remainder to the number of units, that is, break the ten method.