This lesson is to learn the calculation method of decimal multiplication. It is taught on the basis of learned integer multiplication and decimal and integer multiplication, and its teaching growth point is integer multiplication. It is not only the basis of learning fractional division, but also the basis of learning fractional elementary arithmetic and fractional elementary arithmetic. However, how to get the original product after integer multiplication requires a rigorous reasoning process, and the textbook arranges two inquiry activities;

For the first time, in the example 1, think about the three arrows in the dotted box and the meanings of "× 10" and "∫ 100" above to help students experience the reasoning process;

The second time in "Try it", let the students fill in the blanks in the brackets above the three arrows, and write the vertical product on the left for independent reasoning. After two explorations, we compare the decimal places of the product of two factors in each question, and find that "two factors have several decimal places, and the product has several decimal places". On the basis of understanding arithmetic, the operation method of calculating decimal point in product is obtained. At the same time, the calculation method of fractional multiplication is summarized through inductive reasoning.

Analysis of learning situation

There are 5 1 students in this class, including 27 boys and 24 girls. Judging from the final exam last semester, most students have a good grasp of basic knowledge, but some students with 10 have a poor foundation and can't calculate the simplest integer multiplication. In addition, students' autonomous learning ability is average, and they have the habit of cooperative learning. At the same time, students have learned integer multiplication and decimal-integer multiplication before learning decimal multiplication, which lays the foundation for learning decimal multiplication. It should be difficult to learn decimal-decimal multiplication now.

Teaching objectives

1, so that students can understand and master the calculation method of decimal multiplication through independent exploration, and can make relevant calculations correctly.

2. Let students further enhance their ability to explore mathematical knowledge in the process of exploring calculation methods. Cultivate students' reasoning ability and generalization ability.

3. Let students further understand the internal relationship between knowledge, feel the application value of mathematical knowledge and methods, stimulate students' interest in learning mathematics and enhance their confidence in learning mathematics well.

Teaching emphases and difficulties

The teaching focus of this course is to let students understand and master the calculation method of decimal multiplication through active exploration. The difficulty lies in understanding the principle of determining the decimal point position of the product after decimal multiplication is converted into integer multiplication.

Reflections on Decimal Part 2 Teaching of Decimal Multiplication Teaching Contents: National Standard of Jiangsu Education Press, pages 86-87, such as 1, Trial, Practice and Exercise 15, 1-3.

Teaching objectives:

1, through active exploration, let students understand the calculation method of decimal multiplication and make relevant calculations correctly.

2. Let students further enhance their ability to explore the laws of mathematical knowledge in the process of active exploration.

3. Let students further understand the internal relationship between knowledge and feel the application value of mathematical knowledge and methods, thus stimulating students' interest in learning mathematics and improving their self-confidence in learning mathematics well.

Teaching process:

First, the scene import, the introduction of new lessons:

1, the courseware gives an example of the floor plan of Xiaoming's room.

Question: What information can you get from the pictures? What math problem do you want to solve?

How to make it?

According to the students' answers, show the following questions:

(1) How big is the room?

3.6×2.8

(2) How big is the balcony?

2.8× 1. 15

Question: What is the difference between these two formulas and the decimal multiplication we have learned before?

2. Reveal the blackboard title: decimal times decimal.

Second, cooperate to explore and master the algorithm.

1. Explore the calculation method of decimal multiplication.

Preliminary study on (1) estimation;

Teacher: Please estimate the product of 3.6×2.8 first.

Team work: first tell your deskmate what you think, and then communicate with the whole class.

3.6 and 2.8 are regarded as 3,3× 3 = 9, with an area of about 9 square meters.

Take 3.6 as 4, 2.8 as 3,4× 3 = 12, and the area should be smaller than12 square meter.

……

(2) Explore through writing.

Teacher: From the estimation just now, we already know that the product of 3.62.8 is about 9. So what is the actual result? We should also learn how to calculate. The column vertical method is usually used for calculation.

Further enlightenment: recalling the previous method of calculating decimal multiplication, can you calculate both decimals into integers first, so will you do it?

Let the students calculate these two decimals into integers first.

Discussion: After that, is the product obtained the original product? Why not? What are the main changes?

Discuss in groups of four, and then communicate with the whole class.

Students read page 86 of the textbook again to further understand the meaning of the vertical picture of the textbook:

It turns out that both decimals are regarded as integers, which is equivalent to multiplying by 10, and the product is the original 100 times. Just divide the product obtained now by 100, and you can get the correct product.

Q: Is the correct result close to our estimated result? Students who can correctly estimate the results are all great.

2. Further explore the calculation method of decimal multiplication.

Teaching "try"

(1) Can you work out the result of 2.8× 1. 15 according to the method you just solved? Can you borrow the schematic diagram on page 87 to explain your idea?

Students exchange ideas with their deskmates after completing the calculation independently.

(2) Communication with the whole class. Considering these two factors as integers is equivalent to multiplying these two factors by 1000, and the product obtained is 1000 times of the original product. To make the current product equal to the original product, just divide by 3220 to 1000.

Q: Can the current products be simplified? What was the result?

Third, inductive reasoning, summing up methods.

1, guide students to compare examples with the calculation process of "try it".

Observe the factor and product in the example 1 Did you find the relationship between them?

Look at the factors and products in "Try Again". What did you find between them?

What inspiration did you get from it? Can you talk about the relationship between elements and products?

Summary: Decimal times decimal, two decimal places * * * have several decimal places, and the product has several decimal places.

2. Guide students to summarize the calculation method of decimal multiplication.

Teacher: Can you sum up the calculation method of multiplying decimal by decimal now?

Communicate your ideas in groups.

Communicate your ideas in class.

(! ) first calculate the product by integer multiplication.

(2) Look at a factor * * *, how many decimal places are there, starting from the right of the product and pointing to the decimal point.

Note that the results can be simplified.

Fourth, practice and internalize understanding.

1, complete the exercise 1.

Students practice independently and proofread in groups.

2. Complete the second question of "Practice Exercise".

Practice independently and name the board. Collective comments.

Fifth, reflect on the summary and deepen the improvement.

Today, we applied the previous knowledge,

Through active exploration, the calculation method of decimal multiplication is obtained. What have you learned and gained through this process? What else is worth discussing?

6. Finish the written homework: exercise 15 1, 2, 3.

Reflections on the teaching of decimal multiplication

Theory and arithmetic are very important in our calculation teaching. Indeed, reasoning has a positive effect on students' mastery of calculation methods and cultivation of logical thinking ability. However, it is harmful to engage in formal reasoning and ignore students' perception of arithmetic. Formal reasoning seems to be well-founded and rigorous on the surface, but it is not based on students' perception of the calculation process and methods, so it is difficult for students to truly internalize arithmetic and realize the "meaning construction" of what they have learned.

In the current teaching, students are generally guided to understand the calculation method of fractional multiplication from the following aspects according to the arrangement of teaching materials.

1, showing the formula 13.5.

×0.5

2. Guide students to observe the difference between the previous formulas.

3. It makes sense: 13.5→ expand 10 times → 135.

×0.5→ amplification 10 times →5

67.5→ Decrease 100 times →675

However, the teaching effect is very disappointing. When I finished guiding the above transformation process, I asked my classmates to explain why they should do this calculation. Most of them looked at the blackboard, which made sense. But when calculating, they didn't follow the logic at all, especially the poor students made many mistakes. After class, I made a serious reflection. I teach the above calculations in strict accordance with the design intent of the textbook and the requirements of the teaching plan, which is very organized. Why don't I really understand the truth? That's because the calculation process of teaching materials provides reference for teachers and scholars. In actual teaching, we can't copy it, let alone instill the ideas of the textbook into students with what the teacher calls "inspiration", otherwise inference will become a form. To this end, I tried my own teaching methods to guide students to explore independently by using existing knowledge and experience, and to enhance their understanding of arithmetic and algorithms in the process of experiencing feelings. Results According to the teaching method I designed, the students in the class not only mastered the calculation method quickly, but also calculated it clearly, and the teaching effect was very satisfactory.

Reflections on the Teaching of Decimal Multiplication Part III Decimal Multiplication has been taught for two classes. Now let's talk about the feeling after two classes.

I am in the dominant position in the class, and the students take the initiative to find less. I am too impatient. Working for a year, I don't know how to teach.

Decimal multiplication Let the students review decimal multiplication integer first. How much is it to buy three cups?

Students' oral calculation is 3.2×3=9.6.

Then ask a question: Dad wants to buy strawberries again. What information can you get from the picture?

Students know that the unit price multiplied by quantity is the total price.

The formula is 9.9×0.4. First, it is estimated that less than 4 yuan is needed. Then do accurate vertical calculation. This is the focus and difficulty of this lesson.

Students will also understand the calculation process.

But in the process of handing in homework, there are many loopholes, which makes me very scared.

The main problems in the homework are:

There is an error in the vertical form of 1. decimal multiplication: 0 is involved in the operation.

2. There is no 0 at the end of the vertical type.

3. Decimal point is directly pulled down to vertical type or the calculation principle is unclear.

In the above formula, the first picture is 10.5=2. 1×5.

The second picture is 0.86=0.43×0.2, and 0.43=0.43× 1.

The third picture, 10.5=2. 1×5, 6.3=2. 1×3. The first factor is calculated as a decimal and the second factor is calculated as an integer.

4. A new calculation method appears among students. Understand the principle, but can't write simple tables.

In the above formula, 0.0 190 = 0.38× 0.05 and 0.076=0.38×0.2.

How to correct students' mistakes? The following is the default solution.

Hypothesis 1: Students don't understand the principle. How to solve it.

Specific method: say the process.

Let's put a few wrong questions first, so that students can feel the confusion. Can you work out the correct result?

Students solve it by themselves, and teachers guide them.

Decimals directly participate in the calculation process.

Hypothesis 2: Students already know the principle, but they can't write the correct calculation process. Teachers' direct guidance

Specific methods: focus on solving in class. Write some wrong forms for students' reference.

Extra calculation: 000.

In the process of calculation, the size of the number shall not be changed at will.

Implementation effect: Thirdly, students' formats are in good condition, and they can basically write the correct decimal multiplication vertical form except for some students who need further tutoring.

Reflection on Decimal Multiplication Part IV of Decimal Syllabus The purpose of this lesson is to guide students to make use of the experience of decimal multiplication by integers, and then use method of substitution to convert decimal multiplication into integer multiplication for calculation.

First of all, the study of decimal multiplication is introduced by the activity of changing glass, and its function is:

1, which provides the means of subsistence multiplied by decimals. By calculating the area of rectangular glass and introducing multiplication operation, students feel that many problems in life can't be solved without decimal multiplication.

2. Causing cognitive conflicts. When the students listed the formula of 1.2×0.8 to find the area of rectangular glass, the problem appeared. Both factors are decimals, how to calculate them?

3. Take this opportunity to educate students to care for public property and protect the campus environment.

Let students understand the method of multiplying decimal by decimal in independent inquiry and cooperative learning. When 1.2 is expanded to 12 and 0.8 is expanded to 12, the calculation result is 96 square meters. Although this process is not as simple as the textbook, it represents a considerable number of students' problem-solving ideas and should be given in time.

Reflections on Decimal Teaching of Decimal Multiplication The calculation method of decimal multiplication in Essay 5 is summarized as follows: First, the factor 1 * * * has the same decimal, and then several digits are counted from the right side of the product, pointing to the decimal point. When the number of digits is not enough, add "0" to make up, and reflect on the teaching of multiplying decimals by decimals. Its essence is summarized according to the changing law of products.

First of all, by reviewing the method of multiplying decimals by integers, let students conclude that the method of multiplying decimals by integers actually uses the changing law of products, such as the calculation method of 2.05x4, treating them as the multiplication calculation of integers, and then seeing that 2.05 has two decimal places, and the product should be centered on two decimal places. Think about it and discuss 1.2x0.8, how to calculate it?

After students have mastered the calculation method of multiplying decimal by integer, through discussion and discussion, most of them will use the changing law of product in group communication to deduce, and expand the factors of 1.2 and 1.2x0.8 by 10 respectively, and calculate the product as 96. In order to keep the product unchanged, the product will be reduced to 96 1/65438. Therefore, 1.2x0.8=0.96. In this link, students initially perceive the relationship between the decimal places of products and factors. Factor * * * has several decimal places, and the product should be counted from right to left. Reflections on the teaching of decimal multiplication.

Next, I will show you two methods to calculate 6.7x0.3 and 0.56x0.04, so that students can use the method obtained by 0.8x 1.2 to calculate, and then arrange the factor-* * of 0.8x 1.2 with one decimal place, the product of 0.96 with two decimal places, and the factor-* * with two decimal places, 6.7x0. There are four decimal places in the product, so that students can further feel the relationship between the decimal places of the factors of the product in these examples, and then students can naturally come to the conclusion that the calculation method of multiplying the decimal places by the decimal places should be based on integer multiplication first, then count the decimal places from the right side of the product, and when the decimal places are not enough, add "0" to make up.

In the process of consolidating knowledge, the writing format of vertical calculation is highlighted and the calculation principle is briefly described. For example, when calculating 0.29x0.07, students are required not only to write according to the writing format, but also to say 0.29x0.07. First, calculate the product with 29x7, then see that the factor * * * has four decimal places, and then add "0" from the right starting point of the product.

The whole class began to be interested in learning, think positively, solve problems by using the discovered rules, and correctly calculate decimal times integer, and the effect is still good!

The sixth part is about decimal multiplication. Because I teach the fifth grade of the national standard of Jiangsu Education Edition, one of the teaching records inspired me a lot, so I tried it in class according to this teaching idea, and the effect was very good. The following is the information I sorted out by combining the model with my own teaching practice for your reference and exchange.

First, profoundly grasp the teaching content and guide the teaching design.

The textbook summarizes the calculation method of decimal multiplication. Calculate how many decimal places a factor has according to integer multiplication, and then start from the right side of the product and point to the decimal point. In practical teaching, some students migrate and summarize according to the calculation method of multiplying decimal by integer. Look at how many decimal places a factor has, and the product (which means not simplifying) is how many decimal places.

Therefore, the focus and difficulty of this course should be to help students discover and master the law of the change of decimal places in products caused by the change of decimal places in factors, and form a relatively simple method to determine the decimal point of products. On the other hand, teaching methods rely more on the transmission and analogy of old knowledge, allowing students to discover and summarize independently.

Second, create effective problem situations and promote the formation of arithmetic.

1. What situation did it create?

"Compulsory Education Mathematics Curriculum Standard (Experimental Draft)" puts forward that "let students learn mathematics in vivid and concrete situations". We know that the source of mathematics, first, comes from the development needs of the real society outside mathematics; The second is the contradiction from the inside of mathematics, that is, the need of the development of mathematics itself. From this point of view, mathematical situations can be divided into two kinds: life situations, introducing mathematics from life; Problem situation is a situation set from the growth structure of mathematical knowledge itself.

The so-called "effectiveness", that is, the creation of situations in mathematics classroom, should provide support for the learning of mathematical knowledge and skills and provide soil for the growth of mathematical thinking. We should flexibly choose different situations according to different teaching contents.

The textbook of Jiangsu Education Edition takes the calculation of the room area of Xiaoming's house as the situation, which leads to the calculation problem of decimal multiplication that needs to be learned, and then allows students to explore and try. In this way, although it meets the requirements of discovering mathematics from life, applying mathematics and solving mathematical problems, the setting of the situation itself has no substantial influence on the mathematical derivation process of decimal multiplication. On the contrary, decimal times decimal, compared with decimal times integer, the former needs to see how many decimals there are in two factors * * * at the same time, while only one factor in the latter is decimal. The calculation method can be analogized, and the algorithm is essentially the same, which can be verified by the changing law of product. Therefore, the calculation method of multiplying decimal by integer is the derivation basis of the calculation method of multiplying decimal by decimal, and it is feasible to take the growing point of this knowledge as the problem situation.

Therefore, in this class, I adjusted the presentation of teaching materials. First of all, I guide students to understand the calculation method by reasoning and calculating decimal times integer. Then show the problem of multiplying decimal by decimal, and explore it independently. Solve some real-life problems after mastering the methods.

2. How to make the problem situation attractive?

The key of decimal multiplication is to determine the position of the decimal point of the product. Weakening the calculation process of product properly and focusing on finding the relationship between the decimal places of product and factor can ensure the efficiency of students' thinking and avoid the boring feeling of calculation.

Therefore, we can't simply do the topic and summary, but do the mechanical cycle of topic and summary in teaching. I determined the decimal point of the product of decimal multiplication by repeatedly displaying the product of integer multiplication four times. Every time it appears, there are new requirements, and every time it is completed, there are new gains.