Su Jiaoban Volume II, Page 49~50

Teaching objectives:

1. Let students know the quantitative relationship of practical problems such as "How much was it" in specific situations and calculate it correctly;

2. Use students' negative thinking experience to solve the practical problem of finding addend by subtraction to understand the truth of finding the minuend by addend, so as to understand the meaning of addition more comprehensively;

3. Be able to find and put forward the practical problems of "how many" in life, and solve them effectively, so as to cultivate students' problem consciousness and mathematical communication ability;

4. When writing to solve practical problems, develop the habit of marking unit names and answering orally, gain a successful experience, and enhance your interest and confidence in mathematics learning.

Emphasis and difficulty: solving the practical problem of finding the minuend with the help of the existing experience of reverse thinking. Understand the meaning of the question, find the quantitative relationship and determine the method of solving the problem.

Teaching process:

First, create games and introduce situations.

1 Dialogue between teachers and students:

Teacher: Today, the teacher brought presents for everyone. Do you want it?

Health: Yes!

Teacher: Answer the teacher's questions correctly with your little brain, and you will get these gifts.

Teacher-student activities (prepare 9 erasers and put them in opaque boxes)

Teacher: Next, the teacher will let the children grab the gifts in this box.

The students grabbed some erasers, and the teacher told them how many erasers were left in the box. According to the number of students grabbed, say the number of erasers left. ) Teacher: Do you know how many erasers are in the box?

Health: 9 yuan.

The teacher asked: How do you know?

Health: Because the child caught it just now? Brock, the teacher told us there was money in the box? Stop. Add these two parts together and you will get the eraser in the original box.

The teacher demonstrated while summing up: How many erasers do you need? Be sure to combine the two parts you caught with the rest. Blackboard writing: what was caught+what was left = original. If it's 9, let's count it. The number of teachers and students is equal: if you answer correctly, this little gift will be given to you.

Today we will solve such practical problems. Blackboard: How many practical problems are there?

[Design Intention: According to the age characteristics of primary school students, design this game. Students are playing middle school to prepare for learning new knowledge. ]

Second, explore independently and learn new knowledge.

(Courseware display)

1 guess

Mother monkey and little monkey came to the foot of the mountain to pick peaches, and soon they had picked 23 peaches (some pictures appeared, among which the remaining 5 peaches on the tree did not appear, and the blackboard said: 23 peaches have been picked). Please guess how many peaches there may be on the tree. Why? Discuss and communicate in groups.

Focus on two situations: the peaches on the tree are picked, that is, 23; If there are peaches on the tree, the original number may be 24, 25, 26 ... but not less than 23.

[Design intention: First show a part of the picture, let students imagine and guess the original number of peaches on the tree, and pave the way for understanding the quantitative relationship in the question. Mobilize students' enthusiasm for active participation. ]

Say it and do the math.

(1) (Show the remaining five peaches in the situation map) Question: The little monkey hasn't finished picking peaches yet. How many peaches are left on the tree? (blackboard writing: there are 5 left on the tree)

What problem does the topic ask us to solve? (Blackboard: How many peaches are there on the tree? )

How many peaches are there on the tree? What should I do? Why do you count like this? Discuss and communicate in groups.

(2) Summary after discussion: It turns out that the number of peaches on the tree is the total, which is divided into two parts, one part has picked 23 peaches, and the other part has 5 peaches left. If you want to know how many peaches there are, you must combine the two parts and calculate by addition.

(3) Formula calculation. How to form? (Blackboard: 23+5=28 or 5+23=28)

Ask: What does 23 mean? What does 5 mean? What about 28?

What does 23+5=28 (pieces) mean? (Guide the students to say the quantitative relationship in the question, that is, the number picked up plus the remaining number equals the original number) blackboard writing: picked out+remaining = the original number.

3. Talk: From now on, when solving practical problems, in order to express the calculation results clearly, we should write the name of the unit after the number and enclose it in brackets. Usually we say that peaches are one by one, so the unit name of peaches is "one" after 28 (one) on the blackboard.

4. Instruct oral answers and conversations: solve practical problems, and answer the questions in the topic orally after calculation. Question: How many peaches are there on the tree? Who will answer? (Please answer for a lifetime first, and then answer collectively)

Third, practical application.

Dialogue: Through the study just now, we already know how much we want, just combine the collected and the remaining two parts and calculate by addition. There are many such examples in life. Let's go and have a look!

1, CD play, "Think about doing 1"

Say: On Sunday morning, Mingming and Fangfang love to think and play puzzles. What can you tell us from the title after reading this picture? How did you find it?

Question: What question has Fangfang asked us now? (Collective answer) Can it be calculated in form?

Students make their own calculations and name the formulas in class. * * * Same as the revised version.

Question: Why is this problem an addition calculation? (Student) Can you answer the questions in the topic orally? (Student answers)

2, CD playback, "Think about doing 2"

Dialogue: Mingming and Fangfang are studious children, so the teacher will take them to the children's playground on Sunday. Now please look at the picture by yourself. Please tell me the known situation and problems for the rest of your life.

Roll call in the class and tell the formula, * * * and modification. Answer by roll call.

3, CD playback, "Think about doing 3"

Talk: Sunday is really too happy for Mingming. Look, his mother bought him many apples.

Now, please look at the picture yourself. First find out the known conditions and problems in the topic, and then make a calculation.

Please tell me the situation and problems you have known all your life.

Roll call in the class and tell the formula, * * * and modification. Answer by roll call.

4, CD playback, "Think about doing 4"

Dialogue: Mingming and Fangfang are not only eager to learn, but also diligent. They came to the garden to water the flowers. Let's go and have a look! Can you finish this problem by looking at the picture yourself? (born independently)

Roll call in the class and tell the formula, * * * and modification. Answer by roll call.

5. (Summary) Question: Do the four problems we just solved have anything in common?

It is pointed out that these problems are all about combining the removed and the remaining two parts to find out whether it is a * * *.

for instance

Fourth, expand training.

The children learned really well just now. Do you want to accept more difficult challenges? Ok, let's go to "Brave the Wisdom Island". Let's see who can think best!

1, fill in first, and then list the formula.

(1) There are 24 birds flying away from the tree. How many are there in the tree?

Teacher: How do you want to fill it out? Why? There are several birds in the tree, and the ones that fly away should be combined with the rest.

Health: There are five left. Formula: 24+5 = 29 (only)

There are 33 books left in the library. How many books are there?

Teacher: How do you want to fill it out? Why?

Student: Borrow 6 books, and the formula is: 33+6 = 39 (books).

[Design Intention: This expanding exercise is a bit difficult for students, so it is necessary to give students time to think, and pay attention to cultivating students' language expression ability and reverse thinking ability in teaching. ]

Five summary evaluation

What did you gain from today's study?

Summary: We have learned the practical problem of finding how much, that is, combining what has been used with the rest, and we use addition to calculate.

Dialogue: Have you ever encountered these newly solved problems in your life? Can you make up such a question yourself?

Comments: When teaching examples, I pay attention to let students imagine and guess the number of original peaches on the tree with the help of illustrations, teach students to express "part" and "whole" with gestures, let students understand that the original peaches are made up of picked and remaining two parts, and cooperate with language and gestures to help students get the appearance, so that students can say more "What information we already know, what information we don't know, and what are the requirements?" And ask students to fully describe the information they have learned and the questions they have asked. Because such problems are contrary to students' thinking, students often have problems in their initial narration, so teachers organize students to discuss and express their opinions boldly. In the analysis, let students know more about the characteristics of this kind of problems, so as to break through the difficulties and let students gradually understand and solve the problems.

In the teaching process of this course, I attach importance to the analysis of the relationship between the number of students, so that students can find the known conditions and problems of the topic, talk about ideas at length, and strengthen the cultivation of students' language expression ability. The questions of "think about it" and "why" run through. Doing so can not only encourage students to think positively, but also guide them to describe their thinking process in an orderly manner and express their views concisely. However, from the classroom situation, students' language expression ability is relatively lacking and needs to be strengthened.