1. Let students explore the calculation method of decimal addition and subtraction independently, understand the calculation principle and add and subtract correctly.

2. Make students realize the wide application of decimal addition and subtraction in life and study, and realize the instrumental role of mathematics.

3. Stimulate students' interest in learning decimal addition and subtraction, surge the pride of winning glory for the country when they grow up, and improve their initiative and consciousness in learning.

Emphasis and difficulty in teaching

Teaching Emphasis: Decimal addition and subtraction in vertical calculation.

Teaching difficulty: understanding decimal point alignment algorithm

teaching tool

multimedia courseware

teaching process

(1) Scenario introduction

Teacher: Students, do you remember? How is the addition and subtraction of integers calculated? Let's review with an exercise.

(Present multimedia, students complete the exercises by themselves and summarize the calculations)

Teacher: Students, you are great, so today we are going to learn the addition and subtraction of decimals.

(2) Give an example

Teacher: Xiaoli and Xiaolin go to Xinhua Bookstore to buy books on weekends. They have some math problems. How about we help them?

(1) Xiaoli bought the following two books. How much did it cost?

(2) How much is The Mathematician's Tale more expensive than Selected Fairy Tales?

Health: OK.

(Show Xiaoli's questions (1) and ask students to list the formulas)

Teacher: According to the arithmetic of integer addition and subtraction we summarized, think about how to calculate this formula.

Let the students try boldly, discuss in groups and list the vertical styles.

Teacher: What should I pay attention to when calculating decimal addition and subtraction?

Health 1: Pay attention to the alignment of numbers.

Health 2: Pay attention to the alignment of decimal points.

Health 3:

The teacher concluded: the decimal points should be aligned, and the decimal points of numbers should also be aligned.

Teacher: Xiao Li, one more question. Let's have a look (Show Question (2))

Let the students solve it by themselves and recall the places that need attention. )

What should students pay attention to when they finish decimal addition and subtraction?

(3) Practice and consolidate

Do it on page 72 of the textbook.

Summary after class

Students talk about what you have learned in this class.

To sum up: to calculate decimal addition and subtraction, first align the decimal point of each number (that is, align the number on the same digit), then calculate according to the law of integer addition and subtraction, and finally align the decimal point on the horizontal line of the obtained number.

homework

First, calculation.

1.5-0.5= 1-0.9= 2.3+0.6= 0.9+0.8=

1.9-0.8= 3.5- 2.4= 0.36+0.65= 0.96-0.32=

Second, vertical calculation.

20.87-3.65= 3.25+ 1.73=

18.77+3. 14= 23.5-2.8=

Third, solve the problem.

1, Xiaohong buys stationery, pens go to 6.7 yuan, and the pencil case goes to 9.8 yuan. How much will it cost?

2. Dad tied up the newspaper with two ropes1.27m and1.35m respectively. Ignoring the interface, how long is the connecting rope?

Write on the blackboard.

To calculate decimal addition and subtraction, first align the decimal point of each number (that is, align the number on the same digit), then calculate according to the law of integer addition and subtraction, and finally align the decimal point on the horizontal line of the obtained number.

Decimal addition and subtraction teaching plan (2) teaching objectives

1. Knowledge and skills: Understand and master the calculation rules of decimal addition and subtraction, and correctly calculate the addition and subtraction of decimal parts with the same number of digits. Cultivate students' ability of analysis, comparison and induction.

2. Process and method: Experience the learning method of transfer induction through addition and subtraction with the same decimal places and rule induction.

3. Emotion and values: experience the connection between mathematics and life in learning activities, stimulate students' thirst for knowledge, and cultivate serious and hard study habits.

Emphasis and difficulty in teaching

Teaching emphasis: understand and master the calculation rules of addition and subtraction with the same number of decimal places.

Teaching difficulty: understanding the meaning of decimal point alignment.

teaching tool

Multimedia and blackboard writing

teaching process

(1) Activate the experience and get to the point.

Teacher: In the third grade, we began to understand decimals. A few days ago, in Unit 3, we learned the meaning and nature of decimals. I believe everyone must have a deep understanding of decimals. Think about where decimals are used in life.

Students speak freely. (Show courseware)

Teacher: It seems that decimals are widely used in life. For example, when shopping, you will not only encounter decimals, but also encounter the problem of calculating with decimals!

(B) create a situation, independent inquiry

Teaching examples 1

1. Observe and find the problem.

Teachers use multimedia courseware to present the theme map on page 7 1 of the textbook.

Teacher: What information did you get from the picture?

Default: two students go to the book building to buy books, and female students want to buy two books; The little boy wants to buy a 1 dictionary.

Teachers use multimedia courseware to transition from topic diagram to situation diagram in example 1, presenting the unit price of mathematicians' stories and fairy tales respectively.

Teacher: This is the price of two books. Who will watch it?

Teacher: According to what you have read, what math questions can you ask?

Students may ask the following two questions.

(1) How much does it cost to buy these two books?

(2) How much is The Mathematician's Tale more expensive than Selected Fairy Tales?

2. Migrate experience and explore decimal addition algorithm.

Teacher: According to the two questions you raised, think about it. How should it be formulated?

Students list 6.45+4.29 and 6.45-4.29 respectively.

Teacher: This is the addition and subtraction of decimals. In this lesson today, we will learn the calculation of decimal addition and subtraction. (blackboard writing: decimal addition and subtraction)

Teacher: Let's look at 6.45+4.29 first. Let's estimate how much it will cost to buy these two books.

Teacher: This is the addition of two decimal places. How to calculate if it is vertical? According to your experience, think about what we usually do when we meet new knowledge.

Presupposition: Find ways to turn new knowledge into learned knowledge.

Teacher: Conversion is indeed an important mathematical thought. Please use the transformation method, think independently first, try to calculate independently in the exercise book, and then communicate your calculation method with the students in the group after the calculation.

Students try to calculate independently and then communicate in groups. Teachers patrol, call the roll and present different algorithms.

The following situations may occur in the default vertical performance of the student board:

6.45 yuan =645 points

6.45 4.29 yuan =429 points

645 6.45 6.45 10.74

1074 10.64 10 74

1074 integral = 10.74 yuan

3. Exchange reports and talk about liquidation.

Every student on the group discussion board expressed his own ideas.

The teacher leads the students to discuss: which methods are correct? Which method is the same as yours? Tell me what you think.

Students observe each algorithm one by one, fully express their opinions, and clean up the reasons when evaluating.

Default students' answers:

(1) thinks that the first

This is right. According to the experience of calculating a decimal addition, the numbers on the same digit should be aligned. That is, the decimal points should be aligned. Align the number on the unit with the number on the unit, and align the number on the decimal place with the number on the decimal place. Therefore, according to previous experience, to calculate the addition of two decimal places, the numbers on the percentile should also be aligned. (2) first

This is right. Convert 6.45 yuan and 4.29 yuan into? Integral? As a unit integer, that is, decimal addition is converted into integer addition. According to the pen calculation method of integer addition, the sum is 1074, and then the fraction of 1074 is converted into 10.74 yuan. (3) first

The first is species.

Both methods are wrong. Teacher: Let's look at the first one first.

Who else has used this algorithm? Tell everyone what you think.

Teacher: According to your experience in calculating a decimal addition and subtraction, let's discuss it in groups. Why align decimal points?

Students report after discussion, and some may say that the decimal point is not aligned without adding units; Some people may say that the last decimal place should be aligned.

On the basis of students' answers, the teacher leads the students to draw the conclusion that only when the decimal points are aligned can the same numbers be aligned, that is, the numbers representing elements, angles and points respectively are aligned.

Teacher: If we erase the units of yuan, angle and minute, can you tell me why the decimal points should be aligned? Talk to each other at the same table.

Health: Only when the decimal points are aligned can the same numbers be aligned. In other words, digits are aligned with digits and decimals are aligned with decimals.

Teacher: Just now, some students said to align the same numbers, and some students said to align the last decimal places. Which statement do you prefer? Why?

Guide students to try to give a counterexample of 1~2 to show that it is wrong to align the last decimal place, and explain the reasons for aligning numbers on the same number, so as to realize the accuracy of mathematical language.

Teacher: Then let's look at the third and fourth methods. They also align numbers on the same number, but why do you all think these two methods are wrong?

Health: The third method is correct, but the calculation is wrong. The figures in the percentile add up to ten, but I forgot to get to the tenth, 1. The fourth formula is correct in the calculation process, but the decimal point is forgotten in the result.

Teacher: What do you think should be reminded in the calculation?

Health: Every number that adds up to ten goes forward by one. Don't forget to write the decimal point, and the decimal point should be aligned.

Teacher: Is the second method right? Who else has used this method? Tell everyone what you think.

When students communicate, guide them to explain clearly how the transformation is carried out and talk about liquidation. 4. Discuss the comparison and optimization algorithm.

Teacher: Compare the 1 method with the second method. What are their differences and connections?

Guide students to discuss in groups, then communicate with the whole class to reach an understanding and encourage students to express their ideas.

Teacher: Which of these two methods do you prefer? Why?

Guide students to compare and optimize methods.

Design intention: In the whole learning process, students have experienced the process from understanding arithmetic to exploring algorithms. Through independent inquiry, cooperative communication and with the help of existing knowledge and experience, students can understand the arithmetic of decimal addition from concrete to abstract, especially the alignment of the same numbers, so that the numbers on the same counting unit can be added directly.

Teaching example 2

Teacher: It seems that the students can add and subtract decimals. The teacher will test you next.

The multimedia courseware shows the situation diagram of Example 2.

Teacher: This is the price of two books that Xiaolin bought. Who will watch it?

Teacher: According to what you have read, what math questions can you ask?

Students may ask the following two questions.

(1) How much does it cost to buy these two books?

(2) How much is The Mathematician's Tale cheaper than The Magical Nature?

1. Teach experience and explore decimal addition algorithm.

Teacher: According to the two questions you raised, think about it. How should it be formulated?

Students list 6.45+8.3 and 8.3-6.45 respectively.

6.45+8.3=

Students answer vertically and choose different representative methods to act out.

Student discussion report: How to quickly align the same numbers with decimal addition and subtraction?

What's the difference between decimal addition and integer addition? (The decimal addition should finally be aligned with the decimal point above the number. )

8.3-6.45=

Students list vertical solutions and choose different methods to act them out.

Teacher's suggestion: How to calculate the percentile? What if the reduction is not enough?

2. Summarize the calculation method

Teacher: Let's sum up the calculation method of decimal addition and subtraction. (hint: 0 at the end of the column, calculation) and then show it with courseware, so that students can really understand. Note: 1. Align decimal points, that is, align the same numbers. 2. Calculate from the low position by integer addition and subtraction, and the decimal point of the obtained number is aligned with the decimal point above the horizontal line. Reminder: there is a 0 at the end of the number, which should generally be removed.

Design intention: The addition and subtraction of decimals are closely related to the addition and subtraction of integers. They are logically reasonable, and the essence of calculation is to align the same numbers. Therefore, by looking for the connection, students can further clarify the principle of decimal point alignment, and with the help of the internal connection between old and new knowledge, promote students' ability of induction and generalization.

(C) Practice integration, application expansion

1. The students of Bird's Nest and Water Cube must be familiar with it. Let's look at what we don't know.

(1) How many people can the Bird's Nest and the Water Cube hold?

(2) Can the Bird's Nest hold tens of thousands more people than the Water Cube?

Attached answer:

(1) 9.10+1.70 =10.80 (ten thousand people)

(2)9. 10- 1.70=7.40 (ten thousand people)

2. In 2004, Rolex of China and Li Ting won the women's 10 meter platform doubles final. The courseware shows the final report form.

Teacher: What information did you learn from it? After the exchange, ask the students: According to this information, can you ask some questions about addition and subtraction?

See the courseware for the answer.

3. Correct the wrong questions.

Show examples of mistakes in the courseware, and let students judge the reasons for the mistakes and correct them.

See the courseware for the answer.

Summary after class

Teacher: What did you learn in this class?

Teacher-student summary: When calculating the decimal point, first align the decimal point of each number (that is, align the same digit), and then calculate according to the law of integer addition and subtraction, so that the decimal point in the number is aligned with the decimal point on the horizontal line.