The calculation of the method of breaking ten is based on the meaning of subtraction. Students can intuitively understand arithmetic through operation activities and form algorithms. The process of thinking is complicated, and students need to think in at least two steps-reducing first and then adding. Compared with counting and addition and subtraction, it is more difficult to understand, mainly because of students' existing counting habits.

Subtraction formula: minus nine plus one, minus eight plus two, minus seven plus three, minus six plus four, minus five plus five, minus four plus six, minus three plus seven, minus two plus eight.

Other methods: flat ten method

Decimal method is to divide the subtrahend into two numbers, which will be equal to 10 after subtracting the first number, and then subtract the second number with 10 to get the final result. That is, waiting for ten methods.

Ask 18-9, as follows: 18 minus 8, leaving 10, and then minus 1.

The basic principle is to treat 18 as a 10 and an 8, subtract 8 first, and then move 10. 18-9, unit 8 is not enough to subtract 9, so subtract unit 8 first, and it becomes an integer 10. At this time, subtract 1 from this1(because 9=8+ 1), and the answer is 10-65438.