Who has the draft of the mixed operation handout published by Jiangsu Education Publishing House in the second volume of mathematics for the fourth grade of primary school? This is urgent.

Http://www.eku.cc/sx/268,, this is the courseware.

Lecture notes:

The elementary arithmetic of integers and decimals is learned by students on the basis of mastering the elementary arithmetic of integers and the calculation of decimal four. The order of decimal elementary arithmetic is exactly the same as that of integer elementary arithmetic. First, the textbook gives examples of 1 and 2, and briefly summarizes the order of the same-level operation and the second-level operation, and then explains the operation order of the mixed decimal operation with parentheses. In the process of operation, there are many cases of division. Through the teaching of Example 3, it shows that in the calculation process, when the quotient of division exceeds two decimal places, it is generally required to keep two decimal places. The situation of the number of decimal places is more complicated and students are prone to make mistakes. Therefore, the exercises in the textbook should be avoided as much as possible, and they are generally based on three or four steps of calculation. In teaching, students are required to be proficient in calculation, but also to cultivate good calculation habits and consciously use them. In addition, the textbook also pays attention to arranging some text questions and general application questions calculated by decimals to consolidate and improve students' ability to analyze problems.

The first class: elementary arithmetic without brackets.

Teaching content: Example 1 on page 39 of the textbook and Example 2.

Teaching requirements: 1. Let students understand the meaning of first-level operation and second-level operation.

2. Make students master the elementary arithmetic progression without brackets and calculate it correctly.

3. On the basis of students' mastery of integer elementary arithmetic and decimal elementary arithmetic, they can summarize the integer and decimal elementary arithmetic.

4. Cultivate students' serious and rigorous attitude.

Teaching process:

First, review and pave the way

(1) Question: What calculations have we learned? After the students answer, tell them that the four operations of addition, subtraction, multiplication and division are collectively called the four operations. )

(2) Fill in the blanks.

① If there is only () or () in a formula, it should be calculated from left to right.

(2) In an equation, if there are () and (), do () before ().

(3) In an equation, if there are parentheses, first calculate ().

Second, the new grant:

1. Show topic: Elementary arithmetic of integers and decimals.

2. Introduce four operations: the four operations we have learned, including addition, subtraction, multiplication and division, are collectively called four operations.

3. Teaching examples 1.

(1) blackboard example 1: 3.7-2.5+4.63.6× 6 ÷ 0.9

Then ask:

① What operations are there in these formulas?

On the basis of students' answers, tell students that addition and subtraction are called first-level operations and multiplication and division are called second-level operations.

② What is the operation order of these two formulas?

③ If "one-level operation" is used instead of "addition and subtraction" and "two-level operation" is used instead of "multiplication and division", how to describe the operation order?

According to the students' answers, change the narrative of reviewing the blanks.

To sum up, how to describe this sentence?

According to the students' answers, change the narrative of filling in the blanks and show the conclusion of the textbook.

(2) Students complete the calculation of example 1.

4. Teaching example 2.

(1) blackboard example 2: 35.6-5× 1.73, 6.75+2.52 ÷ 1.2, ask again:

① How many levels of operation are included in the formula?

② What is the operation sequence?

According to the students' answers, change the narrative of reviewing the blanks and show the conclusion of the textbook.

(2) Students continue to finish what they have not finished. One student is performing on the blackboard, and the rest are written in books. )

(3) Complete the "Do-Do" exercise below Example 2.

5. Summary: Mixed operation has many steps and is prone to mistakes. To cultivate good habits, we should do "one look, two thoughts, three strokes, four calculations and five checks" when calculating. In the formula without brackets, multiply first and then divide, then add and subtract.

Third, consolidate practice.

Fill in the blanks with 1 and (1). (Show, students answer)

① The four operations of addition, subtraction, multiplication and division are collectively referred to as ().

② Addition and subtraction are called () level operations, and multiplication and division are called () level operations.

(3) In an equation, if it only contains operations at the same level, it should be calculated from (); If there are two levels of operations, the first () level operation should be completed before the first () level operation; If there are two kinds of brackets, count the brackets () first, and then the brackets ().

2. Do it according to page 39 of the textbook.

Fourth, homework.

Exercise 10, questions 1 and 4.

The second class: elementary arithmetic with brackets.

Teaching content: Example 3, Page 40 of the textbook

Teaching requirements: enable students to master the operation sequence of elementary arithmetic with brackets, and correctly carry out elementary arithmetic with brackets, and master approximate calculation in the calculation process.

teaching process

First, review.

1. Calculate the following problem with two decimal places.

( 1)7.05′3.85? 27. 14(2)0.63′0.57? 0.36

(3)4.32? 1.7? 2.54(4)4.67? 0.23? 20.30

Point out the approximate method of product sum quotient and approximate equal sign "?" The use of.

Second, new funding.

1. Reveal the topic: "Elementary arithmetic in brackets".

2. Example 3: Calculation: 3.6? 1.2+0.5′5

Q: What is the operation sequence?

What should I do to calculate 1.2+0.5 first? (parenthesis), what is the operation sequence at this time?

3.6? ( 1.2+0.5)′5

Students try to practice and name the blackboard. When students discover 3.6? 1.7 What should I do if the teacher asks endless questions? If the teacher answers that the quotient of division in the calculation process exceeds two decimal places, generally only two decimal places are reserved for calculation.

After the students practice, the teacher comments and focuses on solving:

=3.6? 1.7′5

2. 12'5 (Why is the equal sign used here? )

= 10.6 (Why is the equal sign used here again? )

Summary: The teacher pointed out the problem on the blackboard, "3.6? (1.2+0.5)'5 What symbol did we use? "(with brackets)" What's the use of brackets here? "(Change the operation order)" What should we do if we encounter infinite division or there are a lot of decimal places in the quotient during the operation? "(Generally, you can only divide it to the third place after the decimal point, and then press" rounding method "to retain two decimal places).

Sometimes you need to change the order of operations in an expression, so you need to use parentheses, but sometimes there are not enough parentheses, so you need to use parentheses' []'

Teacher writes on the blackboard: brackets [], and explains the writing of brackets. For example, in Example 3, calculate (1.2+0.5)'5 first, and then add brackets. In this way, the following formula can be obtained:

3.6? [( 1.2+0.5)′5]

When calculating, you should first calculate what is in brackets, and then calculate what is in brackets.

Explanation: 3.6? [( 1.2+0.5)′5]

=3.6? ( 1.7′5)

=3.6? 8.5 (Why is the equal sign used here? )

0.42 (Why is the equal sign used here? )

Guide students to read.

Third, consolidate practice.

1, judge whether the following questions are correct, and correct any mistakes.

4.06? ( 13.54+ 14.46)-0. 14( 15.38- 1.74)? 3? seven

=4.06? 28-0.4 1= 13.46? 3? seven

0. 145-0.4 1? 4.55? seven