When two numbers with three digits or less are added or subtracted, they are calculated vertically on paper. The following will introduce the basic steps, common mistakes and skills in detail.

Basic steps

1, vertical addition: align two three-digit numbers, add them bit by bit from one digit, and add 1 to the last digit in the case of carry, and finally get the result.

2. Vertical subtraction: the minuend is aligned with the subtree, and the subtraction is carried out bit by bit from the unit. If the minuend is smaller than the subtree, the result is obtained by borrowing from a higher position.

Common mistakes

1, missing borrow or carry in calculation;

2. Alignment error leads to calculation error;

3. I didn't notice the alignment of one digit.

The Art of Computing

1, the rule of the sum of memory components, such as 567 = 500+60+7;

2. Convert the problem into a form that is easy to calculate, such as 643-258 = 643-(200+50+8);

3. Calculate by filling in numbers. First, fill in easy-to-calculate numbers, and deduce unknown values with the help of known results.

Addition algorithm:

1, add two numbers with the same sign, take the same sign as the addend, and add the absolute values.

2. Add two numbers with different signs. If the absolute values are equal, the sum of two numbers with opposite numbers is 0; If the absolute values are not equal, take the sign of the addend with the larger absolute value and subtract the smaller absolute value from the larger absolute value.

3. Add two numbers with opposite numbers to get 0.

4. Adding a number to 0 still gets this number.

You can add two opposite numbers first.

6. Numbers with the same sign can be added first.

7. Numbers with the same denominator can be added first.

Computational relation

In mathematical calculation, formulas include data, operators or operators and calculation results. Therefore, the relationship in mathematical calculation is the theoretical basis that must be clear in the calculation principle.

Vertical calculation of three-digit addition and subtraction is a basic mathematical calculation method. On the basis of mastering the basic steps carefully, paying attention to avoiding common mistakes and using skills can improve the efficiency and accuracy of calculation.