10-9= 1;

1 1-9=2;

12-9=3;

13-9=4;

14-9=5;

15-9=6;

16-9=7;

17-9=8;

18-9=9;

19-9= 10。

Extended data

Decimal method, when the unit is not enough, subtract the subtraction with 10 and add the remainder to the unit, that is, decimal method.

Break the ten-law formula

A dozen MINUS nine, a few plus one; Ten MINUS seven, a few plus three; A dozen MINUS five, a few plus five; One dozen MINUS three, several plus seven; A dozen MINUS eight, a few plus two; A dozen MINUS six, a few plus four; A dozen MINUS four, a few plus six; A dozen MINUS two, a few plus eight.