1, the same digits should be aligned; Number of subordinate units;

2. When the numbers on the same digit add up to ten, you have to go forward 1.

Pay attention to when calculating two-digit subtraction with a pen:

1, the same digits should be aligned; Number of subordinate units;

2. Subtract the number on the same digit, and borrow 1 if it is not enough, as 10.

Extended data:

Law of vertical multiplication:

1, starting from the unit, multiply the first factor by the number on each bit of the second factor in turn;

2. Multiply the number on the second factor, and the last digit of the number will be aligned with the second factor;

3. Add up the multiplied numbers again.

Law of vertical division:

1. Divide by the high order of the dividend. How many factors are there? Look at the first few figures of dividends. If it's not enough, watch another one.

2. Write the quotient on the divisor. If the divisor is not enough, put the quotient 0 on this.

3. The remainder of each division must be less than the divisor. Place the digits of the divisor on the right of the remainder and continue the division.