Teaching material analysis: Example 1 Teaching oral arithmetic of divisible decimal numbers. Draw a formula by dividing the colorful flag scene, and then present a stick figure to help students understand the calculation. The textbook puts forward two methods of oral calculation. Example 2: Teaching oral arithmetic from whole to hundreds, with the emphasis on transferring the methods mastered in Example 1 for autonomous learning.
Teaching objectives:
1. Understand the oral calculation of dividing an integer into ten and hundreds, master the methods of oral calculation and estimation, and correctly perform oral calculation and estimation to solve simple practical problems.
2. Explore the oral calculation method of dividing whole ten into whole ten and hundred, and cultivate language expression ability and application ability.
3. Experience the diversification of oral calculation methods, establish self-confidence in learning mathematics well, and stimulate learning enthusiasm.
Teaching emphasis: master the oral calculation estimation method and be able to make oral calculation estimation correctly.
Difficulties in teaching: understanding the verbal calculation of whole scores and whole scores.
Teaching preparation: multimedia, title card
Teaching process:
First, check the import:
Find a home for small animals and do a quick oral calculation.
Design intention: Review the oral division with divisor of single digits, help students recall the oral calculation method, and prepare for the next oral division with divisor of integer ten.
Second, explore new knowledge.
1. The teacher has 80 balloons in his hand. Each student has two balloons. How many students can he give them?
Question: Who can say how you calculated it?
Default value: 80÷2=40 (pieces)
Because 2×40=80
So 80÷2=40
Q: Who else has different methods?
Default value: 8÷2=4 80÷2=40
2. What do you think?
Default: 8 has four 2s, so 80 has four 20s.
Design intention: create situations, divide by mouth, integrate into life and stimulate students' interest in learning.
Third, explore methods.
1. Example 1
(1) There are 80 colorful flags, and each class is divided into 20 flags. Can you divide them into several classes?
Question: Read the question and say what you know.
Q: Who can make a statement?
Default value: 80÷20
Question: Why do you use division?
Default: Because 80 has several twenties and can be divided into several grades, it is calculated by division.
Question: What's the difference between reading the topic and 80÷2?
Default value: the divisor is an integer 10.
Dialogue: How to calculate this question orally? In this lesson, we will learn oral arithmetic in which the divisor is an integer ten. (blackboard writing)
2. Activity: How to do 80÷20 oral calculations, first think independently, and then communicate at the same table.
3. Designated report:
The default is 1: 80÷20=4, because 20×4=80.
Presupposition 2: Because four 20s are 80, 80÷20=4.
Dialogue: We can understand with the help of stick figures. There are 80 flags here, representing 80 colorful flags, 20 flags are one, and there are four twenties in 80, so 80 divided by 20 equals 4.
4. Point out that the deskmate said.
Q: Are there any different methods?
Default value: 80÷20=4 because 8÷2=4.
Follow-up: What do you think? We can think of 80 as 10. What about 20
Default: Because 8÷2=4, 8 ten divided by 2 ten equals 4.
Say its name.
Summary: When solving this oral calculation, some students use multiplication to calculate division, and some students combine the meaning of division to do oral calculation. You can use any method you like. Since this question is to solve the problem, we have to write an answer.
Design intention: With the help of a stick figure, understand the oral calculation of dividing an integer into ten and hundred, and master the oral calculation and estimation methods. Summarize the estimation methods independently, and cultivate students' ability of generalization, summary and induction.
Students use their previous knowledge to solve new problems, which is called applying what they have learned. Can you combine your previous knowledge to estimate these two estimation questions? Try it yourself and tell your deskmate how you estimate it.
Default: Students solve independently and then communicate.
2.83÷20≈ 80÷ 19≈
Default: 83 as 80, 19 as 20.
6. The students speak very accurately. Can you summarize the estimation method of this kind of problem?
Presupposition: In the division estimation of two digits, the two digits are generally regarded as the nearest integer ten, and then the result is obtained by oral calculation.
(3) Independent investigation
Dialogue: Just now, the students learned the oral calculation and estimation of divisible integers. If you divide an integer by hundreds of dozens to increase the data, will it still be calculated? Please try to solve the problems on the study list.
1. Students try to solve
2. Students write on the blackboard
3. Collective communication
In this lesson, we learned oral division and division estimation, and students used what they had learned before to solve new problems.
Question, great, this sentence is for everyone.
Design intention: let students complete independently with the help of what they have learned, and cultivate the ability of knowledge transfer.
Fourth, consolidate exercises:
1. Do it in the book and calculate the solitaire.
2. The question 1 is on page 72 at the back of the book.
3. Question 3 on page 72 at the end of the book
IV. Question on page 72 at the end of the book 7
Design intention: to consolidate students' mastery of oral calculation and estimation methods of integer division of ten and hundred, and improve the accuracy of calculation.
Verb (abbreviation of verb) abstract
A brief history of mathematics
Blackboard writing:
Oral division of labor
80÷2=4 80÷20=4 (piece) 150÷30=5 (piece)
83÷20≈4 122 ÷30 ≈4
80 ÷ 19≈4 120÷28≈4