The first lesson is addition and subtraction mixed operation
Teaching content: the textbook P 1 ~ 4 pages, such as 1 and P5 do 1, and practice a related exercise.
Teaching objectives:
1, so that students can master the operation sequence of addition and subtraction mixed operations and calculate correctly.
2, in the process of solving specific problems, know the meaning of each step in the formula, and explain the operation order according to the meaning of the formula.
Teaching emphasis: in the process of solving problems, master the order of addition and subtraction mixed operations.
Teaching difficulty: Explain the operation sequence according to the meaning of the formula.
Teaching process:
(1) Introduction to the conversation? Arouse interest in.
Students, what kind of scenery do you think is the most beautiful? Today, the teacher took everyone to Harbin, the ice city. (Courseware demonstration)
Is it beautiful? Appreciate the pictures.
(2) scene expansion? Review old knowledge
Let's go to the world of ice and snow!
1. What are the people doing in the picture? How many activity areas is the world of ice and snow divided into? How many people are there in each district? how do you know
The students observed it carefully. We can know from the picture that there are 72 people in the skating area, 36 people in the water skiing area and 180 people in the ice sculpture area. Think carefully, students. Can you put forward some math problems and solve them according to this information?
2. Communication and feedback
Students are great! According to three pieces of information, you can ask so many questions and solve them.
(3) learning new knowledge? Algorithm exploration
Students, let's go to the skating rink and have a look! Now, please listen to the person in charge of the skating rink: welcome to the skating rink, children. There were 72 people this morning, 44 people left at noon, and 85 people arrived. You also go in and have a look!
Students, do you know how many people are skating in the skating rink now?
Calculate and tell your deskmate what you think?
3. Feedback communication.
( 1)72-44=28(2)72-44+85= 1 13
28+85= 1 13
What does 72-44 mean? What does 28+85 mean?
Tell me which method is good. Why? (Method (2) can write a middle number less, so it is simpler. )
4. Use the formula of method (2).
If the teacher changed the subject, there were 78 people in the skating area this morning, 50 people came in and 37 people left in the afternoon. How many people are there now?
Let the students calculate freely, and then communicate with the whole class.
78+50-37
Say the meaning of each step.
5. Summarize the operation sequence of addition and subtraction mixed operation.
After studying these two problems, let's observe the calculation order of these two problems again. Can you sum them up in one sentence? (Add and subtract, counting from left to right. )
(4) Consolidate new knowledge? Summary evaluation
We almost visited the world of ice and snow. We should go back to school. It's a long way. Let's take a bus!
1, (courseware presented) Let's get on the bus at "Chengnan Station". There are 36 passengers on board, 12 people get off and 15 people get on. How many people are there on the bus now?
(1) Please list the formulas quickly.
(2) After completion, talk to your deskmate about the meaning of each step and what is the operation sequence?
When we got to school, we went to the library to read for a while. Please listen to aunt librarian's introduction: Students, today is really a good day. Many people borrow story books. There are 98 story books in the library. Today, 46 books were lent out and 25 books were returned. Do you know how many story books are there in the library now?
(5) class summary
What have you gained from learning this lesson? What do you think you haven't mastered?
The mixed operation of multiplication and division in the second classroom
Teaching content: textbook P4 ~ 5 pages, examples 2 and P5, do one, do two, and practice one related exercise.
Teaching objectives:
1, by solving specific problems, listing formulas and analyzing the meaning of formulas, let students clearly understand the order of mixed operations of multiplication and division.
2. When students encounter mixed multiplication and division expressions, they can calculate from left to right.
Teaching emphasis: master the operation order of multiplication and division mixed operation.
Teaching difficulties: Let students understand the quantitative relationship of the topic and see the meaning of each step in the formula.
Teaching process:
(A) review the old knowledge
Yesterday we learned the mixed operation of addition and subtraction. Who can tell us the operation order of the mixed operation of addition and subtraction?
1, recall the operation order of addition and subtraction mixed operation. (In the formula with only addition and subtraction, the calculation goes from left to right. Look at the two problems first, and then analyze the operation sequence in combination with specific problems.
2. Talk about the operation sequence and calculation.
25+78-9 1 105-58+46
(B) to open new courses
The students seem to have mastered it well. Everyone applauded to show encouragement. Today, we will go to the "Ice and Snow World" to see if there will be any new situation there.
1, example 2.
"Ice and Snow World" received 987 people in 3 days. According to this calculation, how many people are expected to receive in 6 days?
2. Ask the students to read the questions.
3. What does this calculation mean? (refers to the number of people received every day, calculated by receiving 987 people in three days.
4. Let the students discuss the problem-solving methods in groups. You can understand them with the help of line segment diagrams, list formulas and think about what each step of the formula means.
5. Organize communication:
A step-by-step formula: 987 ÷ 3 = 329 (person) 329× 6 = 1974 (person) comprehensive formula: 987÷3×6.
=329×6
= 1974 (person)
Line chart:? 987 people in three days. How many people will a * * * receive?
Guide the students to draw their own line segments on the blackboard, especially to evaluate the length of the line segment representing the number of people receiving six days. 987÷3 indicates how many people are received in a day.
329×6 means that the number of people received in a day can be calculated by multiplying the number of days by 6.
Which is easier to compare, step-by-step or comprehensive? The comprehensive formula is simpler, and he can write a middle number less. )
b、6÷3×987
6÷3 means that there are two 3s in six days, that is, two 987 people.
6. Summarize the operation sequence of mixed operation of multiplication and division. (Only the formula problem of multiplication and division, the calculation is from left to right. )
7. Summarize the operation order of only addition and subtraction or only multiplication and division in formulas without brackets. (In the formula without brackets, only addition and subtraction or only multiplication and division are calculated from left to right. )
(3) Consolidate and deepen
1, oral calculation.
27÷3×7 ? 3×6÷9 25÷5×8
45+8-23 63÷7×8 24-8+ 10
28÷4×7 ? 35+24- 12 ? 48÷8÷9
Driving a small train, every time you say one, other students will judge whether it is right or wrong. The students in front made a mistake, and the students behind corrected it. The sooner the better. If the students in front are slow, the students behind can answer quickly first.
2, a box of orange juice 48 yuan, Fangfang wants to buy three bottles, * * * How much?
Ask the students to answer the second question. Maybe some students will ask questions that they can't do, and they lack conditions. Guide the students to look at the pictures and find the conditions.
(d) Summarize the improvement.
What do you think you have improved through this course?
Mixed operation of sum (difference) of product quotient of the third kind
Teaching content: textbook P6 ~ 7 pages, examples 3 and P7, Do-Do and exercises related to exercises.
Teaching objectives:
1. Let students master the operation order of two-level operation (without brackets) and calculate correctly.
2. Let students feel the truth of "multiply and divide first and then add and subtract" in the process of solving practical problems.
Teaching emphasis and difficulty: let students understand the operation sequence.
Teaching process:
(a) review of imports
In the first two classes, the teacher introduced some information about the "world of ice and snow" playground. Today, the teacher brought the statistics of the number of visitors to the "Snow World" playground. Let's take a look at this statistical table. What math questions would you ask? Show the following table:
The teacher can prompt them to ask some two-step calculation questions)
According to the students' answers, it shows:
3 days * * * received 987 people. According to this calculation, how many people are expected to receive in a week?
Students answer in columns. And talk about the calculation order.
Introduce a new lesson: On Sunday, mom and dad took Lingling to the "world of ice and snow". Everyone is talking about the "Ice and Snow World" amusement project.
What should you do first at the entrance of the venue? Look, everyone, the playground is here, and the sign is clearly written. Can you understand its meaning and buy a ticket?
Show the scene pictures in the courseware and guide the students to look at the pictures. Question: What do you see from the picture?
(2) Explore new knowledge
1, teaching example 3
(1) Students discuss, exchange information and report in groups.
Who can describe the problem completely in words?
Teacher's guidance, students' answers, teacher's courseware: On Sunday, mom and dad took Lingling to the "world of ice and snow". 24 yuan for each adult, half price for children. How much is the ticket?
Question: How much is an adult ticket? What do you mean by half price? How much is each child ticket? How many adult tickets should I buy? How many tickets for children? What is the problem to be solved?
Question: How much does it cost to buy a ticket? What must I ask first, then what, and finally what?
(2) Column solution.
Health 1: 24+24 = 48 (yuan) 24 ÷ 2 = 12 (yuan) 48+ 12 = 60 (yuan)
Health 2: 24+24+24 ÷ 2
Health 3: 24× 2+24 ÷ 2
Teacher, Q: What is the connection between these three formulas? (The first formula is a step-by-step formula, and the second and third formulas are step-by-step formulas. The meaning of the last two formulas is actually the same. 24+24 and 24×2 are both counting how much are two adult tickets? )
What does 24×2 mean? What does 24÷2 mean?
Let the students answer independently.
(3) Clear the solution method of the comprehensive formula.
24+24+24÷2 24×2+24÷2
=24+24+ 12 ? =48+ 12
= 48+ 12 = 60 (yuan)
= 60 (yuan)
The solutions of the above two comprehensive formulas are given, although both formulas are for buying tickets. How much will it cost? But the writing is different.
(4) Guide students to compare.
What is the difference between the formula of the review question and the formula of Example 3?
Reveal the topic: this is what we are going to learn in this class today. Question: In the formula without brackets, there are multiplication, division, addition and subtraction. What should be counted first?
The students answered, and the teacher concluded: in the formula without brackets, there are multiplication and division, addition and subtraction, and multiplication and division must be calculated first.
2. Q: Can you ask any other questions? Discuss and communicate in groups.
Students may ask:
(1) How much is it to buy 1 adult tickets and three children tickets?
(2) Buy three adult tickets and pay 100 yuan. How much should I get back?
Students independently list the comprehensive formula solutions and tell the calculation order.
3. Comparison: What are the similarities and differences between these formulas and examples?
Students answer, the teacher summarizes and deepens the operation order.
4. Feedback exercise: the first 1 question of "doing" on page 7.
Draw "√" in the same operation order and "×" in different order.
( 1)2×9÷3 (2)36-6×5 (3)56÷7×5
2+9-336÷6×556+7×5
(3) Consolidate and improve
1, tell the operation sequence of the following questions, and then calculate.
203- 134÷2 28+ 120×8
97- 12×6+43 26×4- 125÷5
Let's talk about the operation order of each question first. Please ask four students to perform on the blackboard, and the other students will finish it on their own draft paper. Proofread after completion, and point out any mistakes in time.
Step 2 solve the problem.
(1) Students plant trees. There are 140 students in Grade 4, each of whom plants 2 trees; There are 120 students in grade five, each of whom planted 3 trees. How many trees have been planted in these two grades?
(2) There are 48 apple trees in the orchard, the number of peach trees is twice that of apple trees, and the number of pear trees is more than the total number of apple trees and peach trees 12. How many pear trees are there in the orchard?
(4) class summary
What did you learn from this course? Please ask your deskmate to comment on whether you did well in this class.