In mathematics, when the first-level operation (addition and subtraction) and the second-level operation (multiplication and division) appear in the same formula at the same time, their operation order is multiplication and division first, then addition and subtraction. If there are parentheses, the order of operations at the same level is from left to right. Such operations are called four operations.

Four algorithms:

1, integer addition and subtraction operation rules:

1) Align the same numbers, and then add and subtract the numbers in the same counting unit;

2) Whoever reaches 10 will advance to the next one.

2. Calculation rules of decimal addition and subtraction:

1) To calculate decimal addition and subtraction, you must first align the decimal points of each number (that is, align the numbers on the same digit).

2) Then calculate according to the law of integer addition and subtraction, and finally align the decimal point on the horizontal line in the obtained number.

(There is a 0 at the end of the decimal part of the number, so it is generally necessary to remove the 0. )

3, decimal addition and subtraction calculation rules:

1) When the denominator is the same, only the numerator is added and subtracted, and the denominator remains the same;

2) If the denominator is different, divide it into fractions with the same denominator, and then add and subtract.

4, integer multiplication rule:

1) Starting from the right, multiply the first factor by the number on each bit of the second factor in turn, and the end of the number will be aligned with which bit of the second factor and on which bit of the factor;

2) Then add the multiplied numbers.

(Multiply with 0 at the end of an integer: you can multiply the number before 0 first, then see how many zeros are at the end of each factor, and add a few zeros at the end of the multiplied number. )

5, decimal multiplication rule:

1) Calculate the product according to the law of integer multiplication;

2) See how many decimal places a * * * factor has, and count the decimal places from the right of the number.

3) There is a 0 at the end of the decimal part of the number. Generally, 0 should be deleted.

6. Fractional multiplication rule: multiply the numerator of each fraction as the numerator, multiply the denominator of each fraction as the denominator (that is, multiply the reciprocal of this fraction), and then reduce the score.

7, integer division rule

1) From the quotient of dividend, first look at how many digits the dividend has, and then try to divide the dividend by the first few digits. If it is smaller than the divisor, divide it by one digit as much as possible;

2) Write quotient on divisor and dividend;

3) The remainder after each division operation must be less than the divisor.

8, divisor is an integer fractional division rules:

1) According to the law of integer division, the decimal point of quotient should be aligned with the decimal point of dividend;

2) If there is a remainder at the end of the dividend, fill in zeros after the remainder and continue the division.

9, divisor is a decimal division rule:

1) First look at how many decimal places the divisor has, and then move the decimal point of the divisor to the right by a few places. If there are not enough decimal places, use zero to make up;

2) Then divide by the fractional division of integer divisor.

10, division rule of fractions:

1) The numerator of the divisor is multiplied by the denominator of the divisor as the numerator;

2) The denominator of the dividend is multiplied by the numerator of the divisor as the denominator.