Xinmin Education Publishing House, the teaching record of the first volume of the third grade mathematics of primary school, Preliminary Understanding of Fractions 1. Review the average score. Teacher: On the evening of Mid-Autumn Festival, Yang Yang and Yue Yue are sharing moon cakes. Let's have a look! Courseware shows that one * * * has four moon cakes, which are reasonably distributed to two people. How much is each? A * * * has two moon cakes, which are also reasonably distributed to two people. How much is each? Teacher: Like this, everyone gets the same amount, which is mathematically called average score. Teacher: But there is only one moon cake. Can it be averaged? Health: Yes. Teacher: If you are invited to divide it, how are you going to divide it? Student: Divide a moon cake into two equal parts, half for each person. Teacher: (courseware demonstration method) Can this score be said to be half? Student: No teacher: How to divide it in half? Student: Average score. Teacher: OK, I'll try. Is that so? It can be seen that only the average score can be said to be "half". Courseware demonstration: Divide a moon cake into two equal parts, each half. ) 2. Representing half Teacher: But what numbers should this half be represented by? Come, this classmate. Student: 1/2 Teacher: Students, have you heard of this number? Health: I have heard of it. Teacher: Numbers like 1/2 are called scores. In this lesson, we will know the score (blackboard writing: cognition). Teacher: Divide a moon cake into two parts equally. This is 1/2 of this cake. What about the other one? (It's also 1/2 of this cake) (Synchronous demonstration of the writing of fractions, fractional lines, denominators and molecules) Who does it mean? Can you tell us how the 1/2 of this moon cake came from? 3. Find the rectangle 1/2, take a rectangle, fold it first, and color its 1/2. (music) students' colored works. Different folding methods, why are the colored parts all rectangular 1/2? Health 1: whole life 2: all rectangles are divided into two parts on average, and one part is colored. Summary: It doesn't matter if the folding method is different, as long as it is half of this rectangle, each copy is its 1/2. 4. Practice consolidating judgment: Which of the following figures is colored 1/2. Summary: No matter moon cakes or graphics, as long as they are divided into two parts on average, each part is 1/2. 5. How much do you want to know? Health: 1/4, 1/8, 1/3, 1/6 ... (teacher's blackboard) Do you want to express a score with a number? Please see the requirements (courseware demonstration: fold it first and use diagonal lines to indicate a fraction you want to know. ) is that all right? Can't wait, take out the second picture and start. (Music) Report: How many copies do you divide this number into, and how many are in color? Health 1: I divided it into 8 parts, and the colored part was its 1/8. Teacher: That's good, just two words, student 1: General teacher: Oh. I remember. He divided the moon cakes into eight portions on average, and each portion was 1/8. That's great. Anything else? Health 2: I divided a circle into four parts on average and drew one part, each part is its 1/4. Teacher: Is that all right? This classmate expressed a quarter, in fact, everyone expressed it, right? So everyone has a chance to put your work on the table gently and communicate with each other at the same table, okay? Intra-group communication Students, is it easy to represent a score with a graph? However, if you go deeper, you will find that the knowledge here is not simple. Look, I have collected some of your works, rectangular, square and round. Come on, teacher, let's see who is faster. Exhibition works: 1/4 (1) are different in rectangle, square and circle. Why is the colored part of 1/4? Health: Because they are divided into four parts on average, and one of them is colored. (2) Can different numbers show the same score? (Yes) (3) Can the same graph show different scores? (which students got the circle? Hold high your works, students. Look, there are 1/2, 1/4, and 1/8, collecting works) 6. The comparison score (1) shows the works: 1/2 and 65438+ are represented by circles. Sheng 1: 1/4 sheng 2: 1/2 1/2 stands for what part? 1/4? What symbol is used in the middle? (greater than symbol) (2) Teacher, here is the same circle. If it is used to represent the ratio of 1/8 to 1/2 and 1/4, what would it look like? Who made it 1/8? Take it out and compare it Is it what you think? Verified by students' works. (3) This is a circle. Can rectangles and squares of the same size show different scores? The teacher gave each group the same size of graphics. Who represents the big score? Who said the score was small? Compare quickly, say, go. Intra-group comparison. 7. Write scores. (1) Knowing so many scores, can you still write scores? Ok, take out your finger and write a 1/2 with me. Write a short cross in the middle first, and be careful not to write too long. Write 2 under the short cross, write the middle below, and write 1 above the short cross, which is also in the middle. Can you write? Ok, let's see. (2) Can you use fractions to represent the colored parts in each picture below? (Practice in the book) Is that all right? Open the math book, turn to page 93, find and do the first question, and fill in the scores in brackets. Have you finished writing it? Who wants to say out loud which four scores you wrote? Report:1/31/61/91/8 8. Look carefully at the names of each part of the teaching score. How many parts do they consist of? Just as everyone has his own name, so do all parts of the score. Do you want to know? It's at the bottom of page 94 of the math textbook. See who finds it first. If you find it, look at it carefully. Now, if you close your math book, can you still say it? Confident students, please close your math books. Come on, there is a short cross in the middle, right? (Scoreboard) means an average score of 2? Denominator The denominator is 2, which means equal share? (2 volumes) 1 What is it? The (molecular) molecule is 1, which means one of them. Do you remember? The teacher tested you. What is the part name of 1/6? Are there any questions about the name of the score? 9. Practice the picture estimation first, and then fill in the appropriate score. Firstly, the rectangle 1 1/3 is estimated, and the courseware moving 1/3 verifies that the rectangle is divided into three parts on average. 1/6 estimates that the courseware has been moved by 1/6, and the rectangle is divided into six parts on average. How did it get done all at once? What's the trick? Health 1: 1/3 is twice as high as the following. Through observation and comparison, it is estimated that this is a good learning method. Now, let's look at it completely again. Is the score learned today related to the previous 1? Next question, can it be averaged? Further down, how many points may appear? Health said. When the average number of shares is increasing, the size of each share will become smaller and smaller. Great, let's look at life again, shall we? 10, how much does the picture below remind you of? Photo: French flag (1/3) five-pointed star (1/5) chocolate (1/8) every part is 1/3 of this number. How many people can you eat with? 1 1, Play: Dumex 1+ 1 The milk powder advertising teacher also brought you an advertisement. The content is about this. Dongdong divided a cake into four parts, but when he turned around, he saw eight people. What would he do? Don't worry, just after he solved the problem, a ninth man came. What would he do? Let's have a look, shall we? There is a problem. While watching the advertisement, don't forget to think about how much the pictures in the advertisement remind you of, okay? Come on, let's see who sits most straight. Is it fun? The content of math class is not just fun. How much can you associate the pictures in the advertisement? Health: Can you think of a picture that is related to 1/4? Health: In the first picture, the cake is divided into four parts, and everyone gets a health: Can you think of which picture 1/8 is related to? Health: In the third and fourth pictures, a cake is divided into eight parts, and everyone gets a raw one: Can you think that 1/2 here is 1/2 of the whole cake? Student: No, it's 1/2 of the cake in the little boy's hand. Student: 1/9 If there are 9 people at the beginning and they are divided into 9 parts equally, everyone will get this cake 1/9? 12. Finally, the teacher gave us two scores:1100 and 99/ 100. Can you read these two scores? They can also be simply pronounced as 1% and 99%, hence the following sentence: Genius is 1% inspiration, plus 99% sweat. Teacher Edison: After reading this sentence, tell me, if you want to be 100 successful, only 1 smart is enough? (Not enough) Don't work hard, OK? (No) You have to work hard for 99 copies to get 100 copies of success. 13. What did you learn from this course?