1, so that students can make correct reasoning judgments according to the existing conditions, feel the simple reasoning process, and initially gain some simple reasoning experience.

2. Cultivate students' methodical and well-founded thinking habits, and cultivate their preliminary abilities of observation, analysis and reasoning.

3. Cultivate students' awareness of problems and innovation, develop the study habit of cooperation and communication, and cultivate students' mathematical practice ability.

Teaching process:

Pre-class activities: in pairs, one person flips a coin and the other person guesses the pros and cons of the coin.

[Comment: According to the teaching content, the activities of guessing coins before class are carefully designed, which not only harmonizes the learning atmosphere, stimulates the interest in learning, but also accumulates perceptual experience for the exploration of new courses. ]

First, the introductory teacher: Just before class, we played a guessing game of guessing coins. Is it interesting? Next, let's visit the zoo with Cong Cong, Cherry Maruko and crayon Xiao Xin, and play math activities.

Demystifying the topic "guess"

Second, teaching examples 2

1. Which way should I go? (Courseware demonstration: Cong Cong, Cherry Maruko and Crayon Xiao Xin go to visit the zoo, and they come to a fork in the road. )

Teacher: They have a problem. There are two roads ahead, one of which leads to the zoo. Which way should they go? Students guess, communicate and evaluate, and realize that they can't decide which way to take.

Teacher: Just when they were in trouble, the elf came to help them. It gives such a hint.

The courseware shows that this road (No.2 road) is not for the zoo.

Teacher: Now can you tell them which way to go? Why?

Health: They should take the 1 road, because there are only two roads to the zoo, either 2 or 1. On the basis of students' free speech, the courseware verifies the reasoning process of judgment and demonstrates that three people go to the zoo from 1.

[Comment: Let students guess blindly first, feel the uncertainty of the event, then present relevant information, and experience a well-founded and reasonable reasoning process according to the information. ]

2. What color ticket do you have in your hand?

Teacher: The three of them came to the gate of the zoo and went to the ticket booth to buy tickets to enter the park. Look, here are two kinds of tickets:

Red tickets and blue tickets One is red tickets for adults, and the other is blue tickets for children. Let's play a guessing game with these two tickets. The teacher hid the red and blue tickets in his hand, raised a hand forward and said, "My left hand is not red. Can you guess what lottery ticket I have hidden in my two hands? " what do you think? "

Student: Because there are only two colors of tickets, since the left hand is not red, it should be blue, so the right hand is red. You can also think that the left hand is not red, so the right hand should be red and the left hand should be blue. The teacher shows his ticket and verifies it. Applause rang out in the classroom.

Teacher: "It not only guessed correctly, but also made it clear. It's really good! Everyone has reached out to you, and the teacher wants to give you a present. What is this? There are red and yellow flags on the blackboard. The teacher wants to give you an award. It's not red. What color is it? " Students get the yellow flag on the blackboard, and the teacher asks about the feedback thinking process. Please cooperate with your deskmate and take out the tickets in two colors provided by the teacher before class. One person asked, and the other guessed.

3. What's interesting about Mr. Chen's life?

Teacher: In fact, judging by "no", it is often encountered in life. Let's guess some events about Mr. Chen: Mr. Chen has a child, either a boy or. ...

(Student: Female) Teacher Chen likes skipping rope very much, instead of jumping with his left foot, that is. ...

(health: jumping with his right foot) Teacher Chen's bike has a flat tire, not the front wheel, but ...

(Student: Rear Wheel) Then organize students to cooperate in groups. One person asks questions and the other guesses.

4. Summary The teacher pointed out that if there are two possibilities, we can use "... not ...", either this situation or that situation.

[Comment: The design of teaching activities is organic, allowing students to experience the multi-level mathematical activities of "guessing in investigation-guessing in activities-guessing in life". At the same time, they attach great importance to the interaction between teachers and students. Through the demonstration and guidance of teachers, students can be stimulated to guess and communicate with each other, which can arouse their understanding of mathematical phenomena and experience of mathematical laws to the maximum extent. ]

Three. Teaching example 3

Teacher: Cong Cong entered the zoo and came to the zoo for the first time. Do you want to know where tigers, black bears and monkeys live respectively?

1. Which house do they live in? Show courseware: There are three houses where tigers, black bears and monkeys live. Two animals each say a word. Monkey, black bear and tiger "I live in room 1"/"I don't live in room 3"?

Teacher: According to the information provided by two animals, can you guess which room these three animals live in? Discuss in groups and give feedback.

Health: According to what the monkey said, it can be known that it lives in room 1, and now there are only rooms 2 and 3 left. According to what the tiger said, "I don't live in room 3", we can know that it lives in room 2, so the black bear should live in room 3.

Health: The monkey lives in room 1. Room 3 is either a tiger or a black bear, so the remaining room 2 should be a tiger. The teacher asked the students to evaluate and enjoy the fruits of thinking.

2. Which birdcage do they live in?

Courseware demonstration; Peacock, parrot and ostrich live in three cages. Among them, Peacock introduced the birdcage where he lived: birdcage 1, birdcage 2, birdcage 3? Peacock said, "I live in birdcage 2"?

Teacher: Can you guess what birds live in the cage 1, 2, 3? Why?

Health: No, because according to the peacock's hint, it can be confirmed that the peacock lives in cage 2. But I'm not sure which room is a parrot or an ostrich.

Teacher: Who can be an elf and add a condition of "no" so that everyone can guess which birdcage they live in?

Health: Parrots can't live in birdcages 1.

Health: We know that peacocks live in birdcage 2. And because parrots don't live in birdcage 1, they should live in birdcage 3, so ostriches live in birdcage 1.

Teacher: Who else has different tips?

Health: ostriches can't live in birdcages 1.

Health: We know that there is a peacock living in Bird Cage 2. He said that the bird cage 1 is not an ostrich, but a parrot, so the bird cage 3 should be an ostrich.