[theme]

Mathematics in the third grade of primary school: solving practical problems with two-step multiplication.

[Brief description of teaching materials]

"Solving practical problems by two-step multiplication" is the teaching content of mathematics in the third grade of primary school. This part mainly teaches two-step multiplication calculation to solve simple practical problems. Compared with other practical problems of two-step calculation, the known conditions in this kind of practical problems are often more convenient for different combinations, so the method of solving problems is more flexible. The teaching of this course is based on students mastering the calculation method of multiplying two or three digits by one digit and understanding some common quantitative relations of multiplication. Through this part of teaching, students can not only feel the practical application value of multiplication, but also enhance their awareness of problem-solving strategies and realize that there are different solutions to the same problem, laying a foundation for solving more complicated practical problems in the future.

[Teaching objectives]

1. Knowledge and skills objectives

Students experience the exploration process of two-step multiplication to solve simple practical problems, understand the quantitative relationship of multiplication to solve practical problems in specific situations, and think that starting from known conditions or starting from their own problems can effectively determine the problem-solving ideas and solve practical problems by multiplication.

2. Process and method objectives

In the process of solving problems, students can further cultivate the ability of flexibly combining information to solve problems, understand that there are different solutions to the same problem, realize the diversity of problem-solving strategies, and further develop mathematical thinking.

3. Emotional and attitudinal goals

Experience the close relationship between mathematics and life, enhance the awareness of exploration, improve the ability and initiative of cooperation and communication, gain successful experience and establish confidence in learning mathematics well.

[Key Points and Difficulties]

Teaching emphasis: We can correctly analyze the obtained information and solve practical problems by multiplication.

Teaching difficulty: understanding the relationship between quantity.

[Design concept]

Students are the main body of mathematics learning, and teachers are only organizers, guides and collaborators to help students learn; Teachers' teaching must be based on students' existing knowledge, organize students to practice, explore independently, cooperate and exchange, acquire knowledge in a harmonious atmosphere and establish learning confidence.

[Design concept]

The design of this lesson is divided into five parts: (1) activation experience and preliminary perception. By creating familiar shopping situations, students' interest in learning can be stimulated, and students can refine information and ask questions, paving the way for further exploration and solving problems; (2) Cooperate to explore and solve problems. Let students experience the process of thinking independently and then communicating with others, which can not only show students' original thinking and arouse their enthusiasm for thinking, but also let students listen to others' opinions and improve their understanding. In this way, students' subjective consciousness and cooperative consciousness are cultivated. (3) Try to apply it to deepen understanding. Through a series of exercises, students can have a deeper understanding of the practical problems solved by continuous multiplication. (4) Flexible application and expansion of internalization. Organizing exercises through games that students are familiar with and interested in not only cultivates students' ability to solve problems, but also makes students understand that mathematics comes from life and is used in life. (5) Review and summarize, and experience the value.

[Teaching process]

First, activate the experience and make a preliminary perception.

1. dialogue import.

There are many things in life that need us to think and solve by mathematical methods.

2. Create a situation.

Multimedia shows that Xiaohong went to a sporting goods store to buy table tennis: Xiaohong bought 6 bags of table tennis, 5 in each bag, and then fixed the picture at "a table tennis price of 2 yuan".

3. Collect information.

What information did you learn from the movie just now?

Students speak freely.

4. Q: Based on this information, what questions can you ask? (Students discuss with each other)

For example:

(1) How many are there in six bags of table tennis?

(2) How much does it cost to buy 1 package?

(3) How much are these table tennis balls?

Wait a minute.

Who can answer that? (Name and answer)

5. Show examples.

Can you combine the information you have just learned with the questions?

Students are free to express the meaning of the question.

On the basis of the students' answers, the teacher chose to show them: the price of each table tennis is 2 yuan, and Xiaohong bought 6 bags, each with 5 bags. How much will it cost?

Second, cooperate to explore and solve problems.

1. Organize the investigation.

How to solve this problem? You can solve it yourself first and then discuss it in the group.

2. report and exchange.

Which team will report your solution?

Each group reports freely, and the teacher writes on the blackboard while listening.

Scheme 1: 5×2= 10 (yuan)

10×6=60 (yuan)

Q: What do you think?

Teachers use multimedia to guide students to understand the picture: What does 5 mean? What about 2? Is there a direct relationship between "five per bag" and "the price of each table tennis is 2 yuan"? What problems can be solved according to these two conditions? How much does it cost to buy a bag of table tennis? )

Knowing the price of buying a bag of table tennis, what can you find? How much does it cost to buy six bags of table tennis? )

The teacher then asked: Who can tell me what this method counts first, and then what? How much does it cost to buy a bag of table tennis first? How much does it cost to buy six bags of table tennis? )

Scheme 2: 5×6=30 (pieces)

30×2=60 (yuan)

Q: What do you think?

Teachers continue to guide students to understand pictures, supplemented by multimedia. Q: What does 6 mean? How about five o'clock? What problems can be solved according to the conditions of "5 bags per bag" and "bought 6 bags"? How many are there in six bags of table tennis? )

Knowing how many ping-pong balls are in six bags, what can you find? How much does it cost to buy 30 ping-pong balls? )

Q: What is this method first, and then what? (Say how much are six bags of table tennis * * * first, and then calculate how much are 30 bags of table tennis in buy buy? )

If students have other algorithms, such as:

2×6= 12 (yuan)

12×5=60 (yuan)

The teacher wants the students to talk about his calculation basis.

It can be: Assuming that there is only one ping-pong ball in each bag, it takes 12 yuan to buy six bags of ping-pong. In fact, there are five in each bag, so multiplying by five is the money needed to buy six bags of table tennis.

If the students can't explain why they do this, the teacher can tell the students that this calculation can also calculate the correct result, but the calculation reason is difficult to understand, so you can talk to each other yourself. If this method is meaningless, it is best not to use it.

3. Summarize and reflect.

(1) Q: What is the first solution? What about solution two?

Summary: Although the solutions are different. But the calculation results are the same and can be checked with each other.

(2) Continue to ask questions: Can you tell us in your own words what kind of practical problems we have just solved?

(Title on the blackboard: Solving practical problems by two-step multiplication)

Summary: How to observe and think when solving such practical problems?

Look at the picture carefully, read the text carefully, find out the known conditions, and then find out two directly related conditions to see what you can find. Answer further. )

Third, try to apply it to deepen understanding.

1, the first 1 topic of Thinking and Doing.

(1) Information collection: Multimedia demonstration: Squirrel, rabbit and kitten each transported two baskets of apples, each of which was 20kg.

What information do you learn from the picture?

Student 1: Each basket of apples weighs 20kg.

Student 2: Each car has two baskets of apples.

Student 3: There are four cars here.

Student 4: The required question is: How many kilograms of apples does a * * * carry?

Q: What information is directly relevant? What can I find first according to these two pieces of information?

Students analyze and solve problems independently, teachers patrol and students report.

The teacher shows the answers according to the students' reports. What is the key point? Then what are the different methods?

Correct formula: 2×4×20 or 20×2×4.

=8×20 =40×4

= 160 (kg) = 160 (kg)

Students will communicate and check with each other again.

2. "Think and act" question 2.

(1) Guide students to look at pictures and observe them carefully to get effective information to solve problems.

How many rows of rabbit cages are there? How many rabbit cages are there in each row? How many rabbits are there in each rabbit cage?

Students answer independently.

Collective exchange evaluation.

Correct formula: 6×4×3 or 3×4×6.

=24×3 = 12×6

=72 (only) =72 (only)

If a student directly lists the formula: 6× 12=72 (only), it is ok.

3. "Think and act" question 3.

(1) What can be counted first? What else can you calculate first?

(2) Students give feedback after answering independently.

(3) Q: If we put flowerpots in the teaching building like this, how many potted plants do we need?

Fourth, flexible use and expansion of internalization.

"Supermarket Shopping" game: In our life, carpooling solves many practical problems, such as going to the supermarket to buy things on weekends, and presenting shopping fragments and pictures in the supermarket with multimedia: the unit price and quantity of some items.

Milk: one box 18 bags, each bag of 2 yuan;

Drinks: 24 cans per box, each listening to 3 yuan;

Instant noodles: 30 packets per box, each packet of 2 yuan;

Pencils: 10 per bag, 50 cents each;

……

Activity requirements: Divide the students into several groups according to a group of 6 people. Each group takes turns to select salespeople and customers. The rest of the students calculate according to the customer's shopping needs, and then the salesperson judges whether it is right or wrong.

Five, review and summarize, experience the value

What did you gain from today's study? Is there anything else confusing? Which method do you think is more skilled in solving problems?

Many practical problems in life can be solved by the methods learned today. Please observe carefully after class, find out the math problems and answer them, and then think about what you have learned from them.

Special instructions:

The unit cited in this paper: Xichun Central Primary School in Gaochun County Name: Rui Xiurong Postal Code: 2 1 1300.