First, the teaching objectives
Knowledge and skills to master the order of addition and subtraction, can correctly calculate the addition and subtraction of numbers.
Process and Methods Students experience the process of abstracting practical problems into mathematical problems. In communication and calculation, they can understand and master the operation sequence of the same-level operation, correctly use the operation sequence to calculate, and correctly write off-type calculation.
Emotion, attitude and values stimulate learning interest in learning activities, and students can form a good habit of looking at the operation order first and then calculating.
Second, the difficulties in teaching
Focus on understanding and mastering the operation sequence of the same level operation, and be able to correctly perform off-type calculation.
The difficulty lies in the correct calculation of parting and mastering the writing format of parting calculation.
Third, teaching preparation.
Teaching pictures, courseware, ruler, etc.
Fourth, the teaching process
(A), create a situation, review the old knowledge
As the elf definitely took us to the animal park, we saw a group of small animals, each of whom had a recipe. This situation will lead to:
16+9+8=32- 10-6=25+20- 10=48-8+ 17=
First, assign students to discuss what should be counted first, and then discuss what should be counted. Finally, let the students do the calculation and review the calculation of addition and subtraction.
(B) create situations and explore new knowledge.
Courseware shows examples on page 47 1:
There were 53 people in the reading room in the morning, 24 people left at noon and 38 people came in the afternoon. How many people are there in the reading room this afternoon?
1. Observe pictures and collect information.
Analyze the information and ask questions (How many people are there in the reading room in the afternoon? )
3. Think independently and solve problems (students make calculations independently, and the following situations may occur: Method 1: Step-by-step calculation, 53-24=29 (person), 29+38=67 (person); Method 2: Comprehensive formula, 53-24+38=67 (person).
4. Feedback solution, initial perception (classroom report exchange: what is each step of each method? Teacher writes on the blackboard)
5. Comparative summary algorithm: (class discussion)
It is stipulated that in the formula without brackets, addition and subtraction can only be performed in the order from left to right.
6. Deepen the concept and use calculation.
(1) On the writing format of solution 53-24+38. The teacher will demonstrate the blackboard writing and explain the calculation method while explaining. Note: The equal sign should be aligned up and down.
(2) Sorting out the question: What should I pay attention to when writing? Who can fully explain how this problem was worked out?
(3) Consolidate practice and deepen new knowledge.
1. Explore another solution of the example 1 Now that we know that "9 1 people came to the reading room on this day" and "24 people left at noon", how can we ask "how many people are there in the reading room in the afternoon?" Ask the students to calculate independently, and then report and communicate. List the comprehensive formula: 53+38-24 to realize the rationality of adding and subtracting mixed operations and the exchange of operation sequences.
2. Correct the wrong questions: let the students finish independently first, and then specify the students to explain the reasons for the mistakes.
3. Exercise in the book: Let the students say the operation order first, and then calculate the class communication independently, emphasizing the writing format of unbalanced calculation.
(4) Summarize the homework
Teachers and students conclude, what did you learn in this class today? What did you get?
Homework: After class, continue to ask questions that today's algorithm can solve.
Five, the blackboard design