1, discover, understand and master multiplication and division;

2. The distribution law of multiplication can be expressed in accurate language, and it can be used initially;

3. Cultivate students' initial logical thinking ability such as observation, induction and generalization.

4. Infiltrate the method of "from special to general, and then from general to special" to cultivate students' awareness of autonomous learning, take the initiative to explore and draw their own conclusions.

Teaching emphasis: the significance and application of multiplication and division.

Teaching difficulty: simple calculation by multiplication and division.

Teaching process:

First, create a situation to stimulate interest:

(Ask two students to come to the front) What would you do if you met me at the airport in 20 years?

Health: (angry) happy and excited.

Health 1:: Teacher Song says hello.

Health 2: Hello, Teacher Song!

Teacher: I drew this process with a stick figure on the blackboard. The question is, does Mr. Song have two?

Health: No, it's shaking hands separately.

Health: the law of multiplication and distribution (quietly)

(Design intention: create a situation to attract students' attention, lay a foundation for learning new lessons, and stimulate students' desire for knowledge. )

Second, independent exploration, cooperation and exchanges

Teacher: I am very happy to study with you today. It's spring March, which is a good season for planting trees and greening the environment.

1. Introduce the theme map (tree planting scene and information): each group needs 4 people to dig holes to plant trees, and 2 people to carry water to water the trees; There are 25 groups. How many students took part in this tree planting activity?

(1) Reading comprehension: Let students fully express what they know.

Health 1: It is known that each group needs 4 people to dig holes to plant trees and 2 people to carry water to water the trees; There are 25 groups. Ask how many students will take part in this tree planting activity.

Health 2: There are 6 people in each group.

(2) Analysis and solution:

Students report their own solutions and guide them to explain the reasons for different algorithms.

Blackboard: (4+2)×25×4×25+2×25

2. What are the results of the two formulas? What symbols are used to connect? Read-write equation

Blackboard: (4+2) × 25 = 4 × 25+2 × 25

The formula of (4+2) × 25 = 4 × 25+2 × 25.

In the spring sports meeting, Miss Li wants to order nine sets of sportswear, one set of 58 yuan for tops and one set of 42 yuan for pants, so they need less money?

Oral dosage form, get (58+42) × 9 = 9 × 58+9 × 42 (reading equation).

4. Observe these two groups of formulas, please write some similar formulas.

Every student can write several groups of formulas correctly, and many students have expressed them in letters or graphics. (Three students made mistakes and two students corrected themselves)

projected display

Health1:(1+2) × 3 =1× 3+2× 3.

(3+2)×4=4×3+2×4

( 10+2)×5= 10×5+2×5

(6+4)×5=6×5+4×5

Health 2: (4× 2 )× 3 = 4× 3+2× 3

Health 3: His formula is wrong. It should be the sum of two numbers in brackets.

Health 4: (+) × = × +×

(a+b)×c= a×c+ b×c

a×(b+c) = a×b+ a×c

Division; Try to sum up the rules found in the words.

Student: When two numbers are added and multiplied by the third number, you can multiply the third number by the first two numbers and then add them. 、、、、

What are the similarities and differences between the formulas on both sides of the equal sign?

5. Collective induction.

Catch: Sum and multiply two numbers respectively.

Summary: This rule is universal. The law you found is the "multiplication and division method" that our predecessors in mathematics have studied. (blackboard writing: multiplication table) that is-(the computer displays the following words)

When the sum of two numbers is multiplied by a number, you can multiply the two numbers by this number respectively, and then add the two products, and the result remains the same.

6. Discuss the method of memory multiplication distribution.

Teacher: Multiplicative distribution law is different from multiplicative commutative law and associative law. Let's discuss the memory method of multiplication distribution law.

Student 1: Just like a teacher meets two classmates before class, the teacher shakes hands with two classmates and then summarizes.

Health 2: The letter C outside the brackets is like myself. When I came back from school, I stood outside the door. My father and mother are in the house. After I enter the door, I say hello to my father first and then to my mother. Finally, the whole family sat together.

、、、、、

Students have many ways.

(Design intention: By imitating the writing formula, find a memory method, so that students can understand the essential characteristics of the distribution law and stimulate their interest in learning. )

Third, consolidate new knowledge and try to practice.

1. There is a prize contest in the math kingdom. Can you get those beautiful prizes?

( 12+200)×3=□×3+□×3

15×(40+2)=□×40+□×2

2, math game: find friends

(1) Find the formula with two equal numbers, (show the formula card on the blackboard)

(Design Intention: I * * * showed four groups of formulas, so that students can further consolidate their knowledge and improve their interest in learning while distinguishing right from wrong. )

Question: Are 22×7+ 18 and (22+ 18) ×7 friends? If you want them to be friends, how should you change them?

(2) Arrange the cards and divide them into two groups.

Group a and group b

① 100×3 1+2×3 1 ① ( 100+2)×3 1

② 9×(37+63) ② 9×37+9×63

③ (22+ 18)×7 ③ 22×7+ 18×7

Group calculation competition: girls calculate three questions in group A and boys calculate three questions in group B to see who can calculate quickly.

(Design intent: create conflicts and lead to cognitive contradictions)

Why are these male students slow to respond? Do you think this game is fair? Is there any way you can work out this figure quickly? Guide the students to think and get a simple calculation method: turn the group B problem into another form of multiplication and distribution law, which makes the calculation simple. )

Summary: I can do verbal arithmetic, and I can make up ten hundred, which is relatively simple to calculate.

Using multiplication and division can make some calculations simple.

(Make full use of this link and infiltrate the consciousness of simple operation)

Fourth, apply the law and internalize new knowledge.

(8+4)× 25= 34×72+34×28=

First observe and talk about the characteristics of the formula, then try to calculate, name the board and communicate with the class.

(Design intention: echo before and after, which not only reflects the integrity of the content, but also stimulates students' desire to explore and enhances their self-confidence in learning. )

Five, class summary and evaluation:

In your own words, what are the laws of multiplication and distribution?

(Design intention: to cultivate students' awareness of induction and summary and their ability to express mathematics language. )

Blackboard design:

Powder companion

(4+2)×25 = 4×25+2×25

(a+b)×c= a×c+ b×c

Group a and group b

① 100×3 1+2×3 1 ① ( 100+2)×3 1

② 9×(37+63) ② 9×37+9×63

③ (88+ 12)×7 ③ 88×7+ 12×7