Two-digit addition formula: add 9 minus 1, add 8 minus 2, add 7 minus 3, add 6 minus 4, add 5 minus 5, add 4 minus 6, add 3 minus 7, add 2 minus 8 plus/kloc-0 minus 9.

Subtotal formula for abdication of two digits: minus 9 plus 1, minus 8 plus 2, minus 7 plus 3, minus 6 plus 4, minus 5 plus 5, minus 4 plus 6, minus 3 plus 7, minus 2 plus 8 minus 1 plus 9.

Fast calculation refers to a fast calculation method that uses the special relationship between numbers to perform fast addition, subtraction, multiplication and division operations, and uses a thought and a method to perform addition, subtraction, multiplication and division operations on any number quickly and accurately. This operation method is called speed algorithm and heartbeat algorithm.

It enables learners to quickly and accurately master the fast calculation method of addition, subtraction, multiplication and division of any number in a short time with an idea and a method without any calculation tools. So as to quickly improve learners' quick calculation ability in oral and mental arithmetic.

If you want children to really understand the meaning of addition and subtraction, then you should let them operate in kind, practice constantly and understand from practice. Understanding the meaning of addition and subtraction can really exercise children's thinking.

1, practice the operation in 10, which is the basis of carry abdication operation. The operation within 10 is easy to make clear, otherwise the operation after 10 will be very chaotic.

2. Let children know the structure of two digits, and distinguish between "ten digits" and "unit digits", such as "14", including a "10" and a "4", especially the "1" of ten digits, and understand that it stands for "/kloc-0". ?

3. The operation of two digits is suitable for the combination of "horizontal" and "vertical". The relationship between vertical ten digits and unit digits is more obvious. Instead of telling these "terms" to children, let them understand them through sensibility.