Divide 12 by 10 and 2, then subtract, and the difference is merged with the remainder of the minuend. That is, a 10 is divided by the minuend: first. For example, 12-9 = 3 The thinking process of "breaking the ten methods" is that 1 adds 2 to get 3, and then subtracts the subtraction from 10, and subtracts 1 from 10, and then adds them up.