1000 minus 999 requires abdication subtraction, and the longitudinal calculation method is as follows:

Subtraction should be calculated forward from the last bit. First, if you subtract 9 from 0, you need to borrow 1 from the ten digits, and then the digits are 10-9= 1.

The tenth place is 0, and the unit borrows 1. If you want to subtract 9, you have to borrow 1 from the hundred digits, that is, 10 subtracts the unit first and then 9 is 0.

And so on.

Subtraction by abdication is a special mathematical term, which can also be called subtraction by borrowing. That is, when two numbers are subtracted and the number of digits to be subtracted is not enough, borrowing the previous digit is equivalent to adding 10 to this digit, and then calculating.

Integer addition and subtraction algorithm is as follows:

1, aligned with the same number;

2. Starting from the unit;

3. When the addition reaches dozens, it will be promoted to a higher position; If the subtraction is not enough, subtract 1 from the high position. When this number is added to 10, it will decrease.

Extended data:

Fast addition technique

1 and carry-free addition formula

Two digits plus one digit: write down ten digits first, and then write down the sum of the single digits.

Two digits plus two digits: write the sum of ten digits first, then write the sum of one digit.

Multi-digit plus multi-digit: write the sum of the numbers on the same digit in turn, starting from the high position?

2、? Carry addition formula (be sure to observe whether to carry)

Quick addition technique? The key of carry addition is to push 1 to a higher number of digits. Since it's a definite thing, can you push 1? After observation, you can start counting from the high position.

Two digits plus one digit: write the sum of ten digits plus 1 first, and then write the single digits of the sum of single digits (using the formula of adding within 20)?

Two digits plus one digit: first write down two digits to make up a ten digit after integer ten, and then write down the remaining digits after dividing one digit by one, that is, separate one digit to help two digits make up ten.

Subtraction is the inverse of addition.

References:

Baidu encyclopedia-abdication subtraction

Baidu Encyclopedia-Vertical Computing