I. Definition

Elementary arithmetic refers to an expression that includes four operations of addition, subtraction, multiplication and division. In the third grade, elementary arithmetic usually includes the following three types:

1. Same-level operation: an expression contains four operations of addition, subtraction, multiplication and division, but they are all the same-level operations, for example, 2+3×4= 14.

2. Different levels of operations: an expression includes four operations of addition, subtraction, multiplication and division, but not the same level of operations, such as 2+3×4= 14 and (2+3)×4=20.

3. Parentheses operation: In an expression, there are four operations of addition, subtraction, multiplication and division, and some operations need parentheses to change the priority, such as (2+3)×4=20, 2+3×(4+5)=25.

Second, nature.

1, calculate the same level of operation from left to right.

2. The operations at different levels are calculated in the order of multiplication, division and then addition and subtraction.

3. The operation with brackets is calculated in brackets first, and then outside brackets.

4. In an equation, if there are brackets, the inner side of brackets should be calculated first, and then the outer side of brackets should be calculated; If multiplication or division is preceded by parentheses, count the inside of parentheses first, and then count the outside of parentheses; If there is a plus sign or a minus sign in front of the bracket, the outside of the bracket should be calculated first, and then the inside of the bracket should be calculated.

5. In an expression, if there are three or more operations such as multiplication, division, addition and subtraction, you should calculate multiplication first, then multiplication and division, and finally addition and subtraction.

6. In an expression, if there are three or more operations including parentheses, multiplication and division, addition and subtraction, multiplication and division should be calculated first, then addition and subtraction and parentheses, and finally the outer side of parentheses should be calculated.

Third, application

1, daily life: In daily life, elementary arithmetic is widely used. For example, you need to calculate the total price when shopping, and you need to calculate the travel time when traveling.

2. Scientific calculation: Elementary arithmetic is also essential in scientific research. For example, in physics, chemistry, biology and other fields, complex calculations and analysis are needed.

3. Engineering and Mathematics: In the fields of engineering and mathematics, elementary arithmetic is also very important. For example, when solving some complex mathematical problems or engineering problems, we need to get accurate results through elementary arithmetic.

4. Economy and finance: In the economic and financial fields, elementary arithmetic also plays an important role. For example, when making a company's financial plan or analyzing investment risks, it is necessary to calculate various indicators and ratios through elementary arithmetic.

5. Computer programming: In computer programming, elementary arithmetic is also one of the commonly used operations. For example, when writing a program, you need to carry out various mathematical calculations and control the process operation.

In a word, elementary arithmetic is widely used in our daily life, scientific research, engineering mathematics, economy and finance, computer programming and other fields. By learning and mastering the rules and methods of elementary arithmetic, we can better solve various problems and expand our thinking and ability.