(A) Teaching objectives

1. Make students experience the process of communicating their respective algorithms with others, and be able to skillfully calculate abdication subtraction within 20.

2. Let students learn to use addition and subtraction to solve simple problems.

(B) Teaching materials and teaching suggestions

Textbook description

This unit mainly has two contents: one is the subtraction of abdication, which is referred to as "abdication subtraction within 20"; The second is to solve a simple practical problem with "abdication subtraction within 20" and carry the addition learned before, that is, "using mathematics"

The teaching materials are arranged as follows:

(See what you can do)

The abdication subtraction within 20 and the carry addition within 20 are equally important for further learning mathematical knowledge such as multi-digit calculation, which is the most basic knowledge. Therefore, when learning this part of the content, students must learn the calculation method on the basis of understanding arithmetic, and achieve a certain proficiency through reasonable practice, so as to lay a solid foundation for future study. Learning to calculate and apply it to solving problems in life is very beneficial for understanding the significance of operation, understanding the role of mathematics and gradually improving the ability to solve problems. So calculation and application should be combined.

The calculation of this unit has arranged two examples, but it is actually carried out at three levels.

The first level is to create problem scenes with many pictures such as "selling balloons", "selling windmills", "crossword puzzles" and "ring games", so that students can feel the close connection between abdication subtraction and their life in 20 years during the process of discovering and asking questions, and provide rich background resources for students' study. At the same time, let students experience the process of finding, asking, understanding and initially solving problems in specific situations, feel the role of mathematics and experience the fun of learning, so as to prepare emotionally and psychologically for future study.

At the second level, by systematically learning the calculation method of "ten MINUS nine", the basic learning ideas are constructed for the learning of "ten MINUS several". Example 1 is to play with learning tools, think independently, show various calculation methods and the process of cooperation and communication, and guide students to understand arithmetic and master the calculation method of "ten MINUS nine". Because students have the knowledge base of "addition and subtraction within 10" and "carry addition within 20", they emphasize the methods of "want to add and subtract" and "add and subtract by breaking ten" when embodying the diversity of algorithms. In the practice of "doing one thing", students are also guided to understand arithmetic and master oral calculation methods through the methods of "swinging" and "winding". In comprehensive exercises, in addition to strengthening the training of calculation, we should also pay attention to the combination of calculation and problem solving, so that students can constantly understand the role of mathematics.

At the third level, with the help of the thinking method of "ten MINUS nine" and the method of knowledge transfer, students are guided to learn the oral calculation method of "ten MINUS several" and other questions. Example 2 uses students' favorite "Cats Look at Fish", and leads to two topics, 13-8 and 13-5, to guide students to observe and think from different angles and get different calculation methods. Because students have mastered the "carry addition within 20", they have the basis of "add if they want, and subtract if they want", and the method of "add and subtract if they want" is faster, and the results of two formulas can be calculated at the same time, so the textbook pays attention to guiding students to learn the method of "add and subtract if they want" on the premise of ensuring students' freedom to choose the calculation method. The intention of this arrangement is obvious in the "do-and-do" drills and comprehensive drills. In addition, in the comprehensive practice, it also highlights the flexibility, variability and childlike interest of the practice form; And the organic combination of calculation and problem solving.

This unit continues to permeate some mathematical ideas such as set, function and statistics. For example, the idea that infiltration is set at 1; Questions 4 and 5 in exercise 2, questions 3 and 9 in exercise 3, and so on. Question 7 in Exercise 5 gives a simple statistical table.

In the arrangement of "Applying Mathematics" in the textbook, in addition to a small number of arrangements interspersed in exercises, a large-scale scene diagram (Example 3) with attractive plot, rich resources and diverse topics is specially arranged to guide students to solve practical problems with the "abdication subtraction within 20" and "carry addition within 20" they have learned, and at the same time to consolidate oral calculation. In terms of problem solving requirements, from direct calculation according to the meaning of the question to calculation according to the situation. In the practice of "doing one thing", a comprehensive scene map-"beautiful nature" appeared, which expanded the openness, increased the amount of information and gave students more room for thinking. It guides students to collect mathematical information, find problems, ask questions and solve problems independently based on birds flying in the sky, deer running on the ground and fish swimming in the river, thus cultivating their ability to solve problems by using mathematical knowledge. In comprehensive exercises, the content of "applying mathematics" is generally to guide students to understand the meaning of the problem and calculate it with scene diagrams; Or ask questions in combination with the scene diagram, and then calculate.

Teaching suggestion

1. Attach importance to guiding students to learn mathematics knowledge in specific situations.

Computing teaching often only pays attention to the training of arithmetic, algorithm and skills, but ignores the combination with specific situations, making computing teaching a boring training. Teachers should try to change this situation. When teaching examples of abdication subtraction in 20 years, we can make use of many teaching resources provided by textbooks to make up interesting stories, or suppose a real scene to attract students to come up with results and then lead to calculations. On the one hand, it can arouse students' interest and stimulate their emotional input, and at the same time, it can activate students' original knowledge and experience, such as the meaning of addition and subtraction and the relationship between addition and subtraction. On this basis, they can imagine and think, consciously build their own knowledge and learn calculation methods. With their own experience and knowledge, students can learn new knowledge, remember it firmly, form skills faster and use it more freely. The design of teaching materials has already reflected this intention. Teachers should make full use of the teaching resources provided by teaching materials and develop and design consciously and creatively.

2. Guide students to operate, carry out various forms of teaching activities and learn knowledge.

The characteristics of first-grade pupils are concrete thinking in images, short attention time, love to talk and love to move. Teachers should fully consider the age characteristics of students in teaching, guide students to do more hands, use more brains and open their mouths in specific activities, and mobilize various senses to participate in learning activities to improve learning efficiency. Such as teaching examples 1, 12-9. After the introduction of the specific situation, let the students think first. If they can't think of it, they will take out their learning tools to show it, and then communicate with each other after understanding it. On the basis of comparative absorption, they will improve their thinking and learn calculation methods. In the initial stage of practice, we should also emphasize multi-pendulum, multi-circle and multi-talk, and support students' thinking with images.

3. Diversified teaching of processing algorithms.

Mathematics curriculum standards advocate the diversification of algorithms, aiming at encouraging students to carry out personalized learning and fully demonstrating everyone's learning potential. But learning also has a social side, that is, we should absorb good "nutrition" from communication with others and constantly improve our own ideas. Therefore, while advocating the diversification of algorithms, teachers should also organize communication in time to guide students to establish their own calculation methods in conscious comparison and criticism. For example, when teaching the examples of 13-8 and 13-5, if students are allowed to start thinking, because of their different foundations, experiences and ways of thinking, there may be "breaking ten points", "trying to add and subtract" or even "continuous reduction" and "scoring", but students are organized to fully discuss and demonstrate. This process is actually to turn teachers' "teaching methods" into students' conscious construction methods, so that students can learn more deeply.

4. Use flexible and interesting methods to improve the effect of calculation exercises.

Subtraction of abdication within 20 is an important calculation skill, and it must be smooth and accurate when applied. But this requirement can not be achieved at once, but gradually by the end of the semester. At that time, it is generally required to correctly calculate 8~ 10 questions per minute. Pay special attention to the following questions when practicing: (1) According to the characteristics of first-grade children, practice by using games and competitions, such as "driving a train", "finding friends", "picking apples" and "checking passwords". Practice extensively and take good care of every student. In the process of practice, we should know the situation in time and take targeted measures according to different levels to mobilize enthusiasm and improve practical efficiency. (2) After practicing for one stage, you should select a large number of error-prone topics, such as 17-9, 15-8, 14-6, etc. And make cards or combine them with applications to steadily improve the level of oral calculation. (3) For students who are slow in oral calculation or have difficulty in calculation, they should first find out where their problems are, whether they are unclear or slow in memory, and then try to solve them. Then be patient with them, give them more care and encouragement, educate students around them to respect them and see their little progress, so that they can also have a sense of success, build confidence and make continuous progress.

5. Guide students to apply what they have learned and solve math problems around them.

Mathematics curriculum standards stand at the height of promoting human development, emphasizing that students feel the role of mathematics in daily life and attach importance to the cultivation of application consciousness. In order to achieve this goal, we should guide students to consciously use what they have learned to solve mathematical problems around them and constantly improve their ability to solve simple problems. For example, "Do it" at the back of Example 3 provides a picture of "beautiful nature" in the textbook, which contains a lot of mathematical information and can be asked from different angles. In teaching, teachers can inspire students to observe and discover independently and ask different questions on their own initiative; Then collect information and data according to the question to explore and answer; Finally, exchange the results and improve the answers. From this complete process, let students understand the role of mathematics and experience the fun of solving problems.