Teaching difficulties: correct estimation and cultivate students' estimation consciousness.
Teaching preparation: multimedia courseware teaching process: 1. Teachers who value creating situations and feeling estimation: the school brigade department should organize our third-grade students to go to the movies and plan to choose the North Theater. Look, this is the North Theater (courseware demonstration) Teacher: What information did you find? What questions can I ask? Student Questioner: Everyone's questions are very good. The teacher also has a question. Do you agree with me? Question: If 350 students come to the movies, can they sit down? ) Teacher: Do you think the teacher's problem can be solved? How to solve it? Have you thought about it? Somebody say something. Health: Count the total number of seats and you'll know if you can sit. Teacher: How do you figure out how many seats a * * * has? Can you be specific? Student formula: 22× 18 teacher: (doing the problem) but we haven't learned the calculation method of two-digit multiplication? It is helpful for us to recall what we have learned before. (Guide students to recall the estimation of previous research and feel the value of estimation in real life. ) teacher: in life, sometimes we don't need to calculate the result accurately, we can use estimation. Today, we are going to learn the multiplication estimation of two-digit numbers. (Writing on the blackboard) 2. Cooperate and exchange, explore estimation methods. Discuss how to estimate in groups. Teacher: Now, please study in groups. What is 18× 22? Can 350 people sit down? Students discuss in groups, teachers participate in groups, listen to students' ideas, guide students to communicate and learn together with students. ) 2. Reporting method Each group sends representatives to report the estimation method of this group to the whole class. Method 1:18 ≈ 20 22 ≈ 20× 20 = 400 Method 2: 18 ≈ 20 22× 20 = 440 Method 3: 22. (rounding to round off) (2) estimate by number; (3) finding the interval; The method of "ending in one" is to take two factors as a smaller integer and a larger integer close to it, and then multiply them to determine the approximate range of the product. Teacher: The estimation of multiplying two digits by two digits only needs to determine the range of the product, and the estimation strategies are diverse, as long as they are reasonable. Third, the application of estimation, solving the problem 1, estimation challenge The students learned the multiplication estimation with a factor of two digits. Then the teacher will see who has learned the most solid knowledge today. 43× 31≈ 52× 78 ≈ 58× 63 ≈102× 42 ≈ 2. Check whether the following two formulas are correct by estimation? 47× 52 = 341469× 51= 29923. Students illustrate the application of estimators in our lives: in fact, estimation is not only useful in our mathematical calculations, but also useful in many places in our lives. Can you give an example of using estimation multiplication in our daily life? (For example, students contact life) 4. Using estimation to solve problems Teacher: Everyone speaks very well, so we will use estimation to solve two practical problems in life. (1) Courseware shows 59 pages of teaching materials and achieves: one page has 23 lines, each line has about 22 words. How many words are there in one page? ) Students report after thinking independently. (2) Courseware demonstration: Mr. Wang wants to buy school uniforms for 49 students in a class of three years, each set of school uniforms is 104 yuan. Think about how much money Mr. Wang will take to buy school uniforms. After reading the questions, exchange reports at the same table and talk about how you estimate. Teachers show accurate results and guide students to reflect, adjust and compare. Teachers: After seeing this accurate result, look at these estimation methods and processes. What do you think? What are you going to say? Teacher (student report): When solving practical problems in life, we should analyze them in detail. For example, when we go shopping with money, we should consider what we left behind when estimating, and we should bring more money, not just the estimated amount. Teacher: In real life, is there a situation where we can only estimate more than less? Buy cloth for clothes, curtains, etc. ) teacher: so, in real life, is there any situation where we can only estimate less and not more? Let me see: a train has 19 knots, each with a load of 56 tons. How many tons of goods can this train carry? Save your homework and the students will think about it after class. ) Fourth, the whole class summarizes and expands. There are many teachers studying with us in this class today. Please estimate how many teachers are on the scene. (Students estimate the number of teachers) Are you happy that so many teachers have seen your excellent performance? Then report what you have learned, gained and learned in this class to the teachers and students present, so that everyone can share your joy in acquiring knowledge, ok? Teacher's Summary (Student Report)