When the number of units is not reduced enough, you need to borrow 1 from ten units, which is equivalent to borrowing 10, 10- 1=9, and the subtraction of the number of units is equal to 9.
The decimal digit is 2, 1 borrowed one digit, so now its decimal digit is 2- 1= 1, and after subtracting the decimal digit, it is 1- 1=0.
The last number is 9.
There are three ways to do this.
Addition is the method of adding ten, and subtraction is the method of breaking ten equals ten. We only talk about breaking the ten laws, and some versions talk about the flat ten laws.
It will be clearer to explain with pictures.
Generally speaking, it is 10 when you break primary school and Osuka, but some decimal exams are also 10, so you can master them flexibly and train more.
Violation of the Ten Laws.
Let me give you an example.
14-9=() 14-9=4+ 1=5
15-8 = ()15-8 = 5+2 = 7 I see, I can master it quickly without analogy.
Ten-step method.
The difference between the law of breaking ten and the law of flat ten is that the law of breaking ten is to reduce first and then add, while the law of flat ten is to reduce continuously. In the process of doing the problem, teach the child which method to use, and he can use which one he likes.
Fourth, the application problems of addition and subtraction are very characteristic in the first and second grades of primary school. Children should be taught to grasp the main words to judge whether they are addition or subtraction.