First of all, talk about textbooks.
1, teaching material analysis
The estimation of two digits multiplied by two digits is the content of Unit 4, Book 6 of Nine-year Compulsory Education and Six-year Primary School Mathematics. It is taught on the basis that students learn the written calculation of multiplying two digits by two digits. Pay attention to cultivating students' estimation consciousness and ability. Mathematics curriculum standard points out that "estimation plays a very extensive role in daily life and mathematics learning, and it is of great value to cultivate students' estimation consciousness, develop students' estimation consciousness, develop students' estimation ability and make students have a good sense of numbers".
Multiplication estimation is not a single estimate of the divisor, but requires students to learn not only what the estimate is about, but also the range of the estimate, that is, what the estimate is greater than and less than. Multiplicative estimation is a difficult point, and the arrangement of the teaching materials is as follows: Examples guide students to find the "approximation" in the problem by creating the pasture situation that students like, and cultivate their observation ability. Then, through thinking, communication, guidance and summary, they are expressed in language, pointing out two different estimation methods, that is, the range of the estimated number and what the approximate number is. And consolidate the learning content through a series of exercises.
2. Teaching objectives
Using the concept of new curriculum standards, according to the characteristics of teaching materials and the reality of students, I have formulated the following teaching objectives:
(1) By exploring the estimation method of two-digit multiplication, we can estimate what the product ratio of some two-digit multiplication is.
② Choose different estimation methods reasonably, solve corresponding practical problems in specific situations, further develop mathematical thinking and improve problem-solving ability.
3. Teaching emphases and difficulties
Explore the estimation method of multiplying two digits by two digits.
4. Teaching preparation: multimedia courseware and digital cards.
Second, talk about teaching methods and learning methods.
1. In the teaching environment, create a suitable teaching situation that is conducive to students' active knowledge, organize teaching in different forms, let students feel knowledge in the process of autonomous learning, and provide conditions for students to process and apply information. Help them really understand and master mathematics knowledge and skills in the process of independent exploration, and improve their ability to answer practical questions.
2. In the guidance of learning methods, I attach importance to the application of observation, discovery and discussion, fully mobilize students' various sensory organs, help students think positively, develop students' intelligence through multimedia teaching, cultivate students' good thinking, and believe that they have the ability to discover and acquire new knowledge.
3. In teaching, strictly abide by students' cognitive laws, organize teaching reasonably, and cooperate with the application of modern teaching methods to attract and guide students to roam freely in mathematics space.
Third, talk about the teaching process
Proper goals and scientific methods are the premise of successful teaching, but the key to truly realize the teaching goals lies in the teaching process. In this lesson, I designed the following links:
(A) situational import
"Showing an example," the teacher explained, "is obviously an invitation to visit his beautiful ranch." Who will introduce him? Listen carefully and see what you can learn from the pasture.
Ask the students to list the formulas:
29×42=
[This link is based on the ranch situation that students are interested in. While consolidating the multiplication of two digits, it can stimulate students' interest in learning, lay a good foundation for the next teaching and effectively promote the teaching effect. ]
(2) Exploring methods
1, before the calculation, the teacher classified the questions. Please estimate first. 1 day, what is the maximum weight of Ming Can Mingjia milk? How many Jin can I squeeze at least?
Discuss in groups and exchange their estimation methods.
2, the whole class communication:
(1) can produce at least 800 kilograms of milk [how to estimate? It is estimated that the number of 29×42 is above 800. Why use the word "many"? (Looking down at the numbers, 20×40=800. )]
② Maximum milking capacity 1500kg [How to estimate? It is estimated that the number of 29×42 is less than 1500. Why use the word "many"? (Look at all the figures, 30×50= 1500. )
3. Ask the students to estimate the approximate and closest kilograms of milk that Mingming milks in a day?
Student exchange: closest to 1200 kg. [How do you estimate? It is estimated that the number of 29×42 is around 1200. Why use the word "left and right"? Think of all the numbers as integers close to it, 30×40= 1200. )
The estimation method should be clear and detailed, so that students can clearly understand how to estimate. )
4. Calculation verification:
Is there any way to verify whether our estimate is correct? Please have a try. Students who do well first talk about what counts and what counts.
Remind students to pay attention to the continuous carry in the process of vertical calculation.
Contrastive communication: how to treat the results of comparative pen calculation and estimation?
(the third, the closest; The range of the formula is estimated by 1 and 2).
5. Note: The estimation of multiplying two digits only needs to determine the range of achievement and estimation strategy.
It is diverse, as long as it is reasonable. If the multipliers are regarded as integer tens close to them, the estimation results will be more accurate.
[The design intention of this link: The problem of this link is clear in the teaching process, which disperses the difficulties. The estimation of multiplication is divided into two parts, one is approximate estimation, and the other is range estimation, which is discrete first and then summarized, which conforms to students' cognitive law and is easier for students to master. ]
(3) Consolidate and deepen
1, the second question of "think about it and do it"
40×2030×5060×30
47×2334×5868×35
50×3040×6070×40
(1) Each group has 3 questions, the upper and lower 2 questions can be calculated orally, and the middle one should be calculated vertically. Please select one of the questions to calculate.
(2) Independent calculation. Then compare these three questions. What did you find?
(3) Tell me about your findings.
(The number of middle formulas is greater than that of upper formulas and less than that of lower formulas, so the upper and lower formulas can be used to estimate middle formulas. )
(4) How close is this formula? Let's estimate. (Student assessment, classroom communication)
Let's focus on the middle of question 3, where there is a middle number like 35. When this number appears, we usually look at another multiplier to see which integer it is close to. If it is big, then we should look down on 35, if it is small, we should look down on 35.
2, the game: choose a choice ("think about it" question 3).
Before class, give each student digital cards such as 1800, 2800, 3500, 4800, 1000, 1800, 600, 1200.
Let the students play the game of finding friends. If you think that the number in your hand can be filled in the brackets shown by the teacher by estimation, please stand up.
The teacher showed them one by one.
24×53 is greater than () and less than (); About ()
(The question 1 can guide students to complete it, so that students can clearly understand the meaning of the question and know that the part 1 is the estimated range; The second part is approximate estimation. )
37×65 is greater than () and less than (); About ()
28×32 is greater than () and less than (); About ()
The number of 76×59 is greater than () and less than (); About ()
Let the students who choose right or wrong tell the reasons.
Timely feedback.
Summary: The approximate range of the product can be determined by treating the two multipliers as smaller integer decimal places and larger integer decimal places. The multiplier is regarded as an integer ten close to it, and the estimation result is the closest.
3. Volume 37 Question 4
Teacher: Actually, estimation is not only useful in our mathematical calculations, but also in many places in our lives. Choose familiar writing examples in students' daily life and let them know.
Show me the problem.
Tell me what math information you have learned.
How many words do you think there are here? (Students' formula estimation)
Class feedback.
4. Question "Think about it and do it" 5
What information do you learn from the picture?
What kind of basketball do you think he will buy? what do you think?
(1)48×24≈ 1000 (yuan)
(2)38×24≈800 yuan
(3)28×24≈600 yuan
Summary: According to the specific situation in life, choose different methods to estimate. The second one is more suitable.
【 The exercises in this lesson are divided into three categories: special exercises, basic exercises and comprehensive exercises. The exercise design is targeted, hierarchical and ideological. This not only stimulates students' interest, but also trains students' thinking and develops students' personality, which is conducive to deepening students' understanding of new knowledge. ]
Fourth, summarize and extend.
What did you learn from today's study?
Introduce "You know what?"
Verb (abbreviation for verb) assigns homework.
Six, say blackboard writing
Blackboard writing is a miniature teaching plan. Good blackboard writing can make the finishing point, help to organize knowledge and bring it into the knowledge structure, and also provide clues for future memory. In this lesson, I design the blackboard like this:
estimate
( 1)20×40=800
(2)30×40= 120
(3)30×50= 1500