Pay attention to the vertical addition and subtraction in the second grade of primary school: ten digits to ten digits, one digit to one digit.

Vertical subtraction: when subtraction is not enough, borrow a digit forward as ten,

Vertical addition: if everyone adds up to ten, they will advance one. Ten digits into one is ten, and one hundred digits into one is one hundred.

For example:

Extended data:

Vertical precautions for multiplication and division:

1, multiplication

The 1 bit of one number is multiplied by the 1 bit of another number.

It should be added to i+j- 1 bit of the product.

For example:

Step 2 separate

For example, 42 divided by 7. On a scale of 4 [from high to low]. When calculating the division vertically, start from most significant bit, such as: 42 from most significant bit 4; If it is not divisible, such as: 4 is not divisible by 7, then use the highest bit and the next bit to synthesize a number to be divisible until it can be divisible by the divisor; For example, if 4 can't be divided by 7 in 42, then 4 and 2 are combined into a number. If 42 is divided by 7, the quotient is 6.

For example: