For example: 205- 189, the column is vertical, and the first step number is 5-9, which cannot be subtracted, so it is necessary to borrow from the ten digits of 205, but the ten digits of the minuend 205 cannot be borrowed. At this time, you need to continue to borrow from the high position, that is, from the hundred places, then the hundred places become 1, and the ten places borrowed from the hundred places. The decimal digit of the minuend becomes 9, the unit is now 15, the calculation is 15-9=6, and the decimal digit is 9-8 =1; Hundreds: 1- 1=0, so the calculation result is 16.