Teaching content: Lesson 1, Unit 4, Grade Four Mathematics, Beijing Normal University Edition.

Teaching material analysis: The lesson of "Multiplying Three Numbers by Two Numbers" is taught on the basis that students master the multiplication of two digits. The arithmetic sum algorithm of two-digit multiplication will be directly transferred to three-digit multiplication. Learning this part will help students master the calculation method of integer multiplication in an all-round way and lay a good foundation for further study of decimal multiplication.

Analysis of academic situation: Students have learned to multiply three digits by one digit and two digits by two digits in the third grade. However, the written calculation of three digits multiplied by two digits is completely consistent in arithmetic and algorithm compared with the written calculation of two digits multiplied by two digits. Therefore, students will not find it difficult to understand and explore mathematics and algorithms. However, due to the increase of factor digits, the difficulty of calculation will increase accordingly, and various situations will appear in calculation.

Teaching objectives

Knowledge and skills:

1、 ? Make students master the writing method of multiplying three digits by two digits.

2. Cultivate students' analogical transfer and word computing ability? Process and method:? Make students experience the whole process of writing, multiplication and calculation, master the methods, emotions, attitudes and values of calculation and calculation; cultivate students' good study habits of careful calculation. ? What is the point? Make students master the calculation method of multiplying three digits by two digits.

3. Difficulties? Make students master the calculation method of multiplying three digits by two digits and calculate correctly.

teaching process

First, review the import;

1, oral calculation:? 23×30=47×20=42× 19≈? 58×4 1≈

2. Write 34×62=? 45× 12=

What is the method of writing?

3. Reveal the theme of blackboard writing.

Second, explore new knowledge.

? 1. Silent reading problem. What mathematical information do you know? What are the questions that must be asked?

Watch the onion video.

? Grade three 1 class, want to go to the island. There are three choices, which one is the most suitable?

2. What's the answer?

3. Why use multiplication?

4. How to calculate 3 12×2 1:

(1) estimation? Teacher: Can you estimate the approximate range of 312x21?

How do you estimate the group discussion?

? Who would like to share your estimation process and ideas with us?

Health: Let 3 12 be 300,300× 20 = 6000, so I think the third scheme is no problem.

(2), written calculation? Teacher: This student is very thoughtful. Does he estimate the product of 3 12×2 1?

Let's discuss what is 3 12×2 1?

So how to accurately calculate the product of 3 12×2 1?

Student: Use vertical calculation.

Teacher: That is to say, write multiplication (blackboard writing).

Teacher: So how do you calculate the product of 3 12×2 1 vertically? Try to calculate it in the exercise book first.

Students try to calculate, teachers patrol, find classmates to perform, and tell their own calculation methods.

Vertical calculation? Let's do it together. Write down several different situations of students' mistakes on the blackboard. )

Teacher: Let's look at the vertical posture of these students. What is the difference? Do you think what that classmate said is right? ?

? Teacher: What does the product of 1 and 3 12 mean?

Health: Choose A, which stands for 1 3 12.

Teacher: Good. Then how to calculate? One digit has been worked out, but how about ten digits? What does the decimal number 2 of 2 1 mean? Where should I write 2 times 2 in 3 12?

Write it in the tenth place, because 2 is in the tenth place, and the same numbers should be aligned? (Students' expressions here may be irregular, and they may say "2 here is 20", so the teacher should guide them.

? Health: the product of 20 times 3 12 is written in the tenth place, because 2 is in the tenth place, and the number of digits should be aligned with 2? Teacher: What should I write at last? ? Student: Add up the two products.

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Teacher: Now, back to our question, which island should we choose?

Third, think seriously, talk about gains and sum up.

Teacher: What did you learn today?

Student: The vertical calculation of three digits multiplied by two digits? Teacher: Now who can help us summarize the steps and precautions of vertical calculation of three-digit times two-digit number?

Health:? (1) The three-digit number is multiplied by the number on the two-digit number, and the last digit of the number is aligned with the single digit of the two-digit number.

(2) Multiply the three digits with the number on the two-digit tens of digits to obtain that the last digit of the number is aligned with the two-digit tens of digits.

(3) Then add up the multiplied numbers twice, and pay attention to all 11%.

Fourth, homework:

(1) Math book "Do it" on page 47.

(2) Exercise 8 1 and 2.