1, two-digit multiplication rule

Integer multiplication starts with the lowest bit, and two-digit multiplication is twice the product. Multiply the number of units by several 1, and the last digit of the product is the number of units. Ten digits are multiplied by dozens, and the last digit of the product is ten digits. Calculate the correct number of digits and add the two products.

2, two-digit multiplication

It is not difficult to multiply two numbers. There are three points in the calculation process: the multiplier must be calculated first and then multiplied by ten digits. The last digit of the product is the key and must be opposite to the ten digits; After the two products are added up, calculate the number of layers in your mind.

3, multi-digit multiplication rule

Integer multiplication starts from the low bit and several numbers are multiplied several times. Multiply the number of units by several 1, and the last digit of the product is the number of units. Ten digits are multiplied by dozens, and the last digit of the product is ten digits. Calculate the correct position and add several products together.

4. Decimal addition and subtraction

Decimals are added and subtracted regularly, and the same numbers should be aligned. One for one, ten for ten. ..... ten to ten, percentile to percentile. ..... In short, the decimal points should be aligned. The calculation result is decimal, and the zero at the end should be crossed out.

5. Invariance of quotient

Dividend and divisor are multiplied at the same time, and the multiplication factors should be the same. Divider and divisor are divided by the same number. In addition to the multiplication and division of 0, the invariance of quotient should be clearly remembered.