Dear judges and teachers:
Hello everyone!I am the No. 4 candidate in the interview for primary school mathematics, and the topic of my trial lecture today is "The change of decimal size caused by the movement of the decimal point".
1. Introduce new courses.
Teacher: Hello classmates!Have a seat.
Teacher: Students, at the beginning of class, let's take a look at a piece of "Monkey King: Havoc in the Dragon Palace". Have you noticed, the length of the golden hoop stick can be changed, the teacher asked the great sage last night, and he said that the shortest time for the golden hoop stick is 0009m, which can be changed to 009m、0.9m, 9m, did the students find any math problems?That's right, yes, the decimal point has moved, so what does the decimal point move have to do with the length of the golden hoop stick?
Teacher: It's okay to see that everyone is at a loss, I believe that through today's Xi you will definitely find something, today we will take a look at "The Decimal Point Movement Causes the Change of Decimal Size".
Second, ** new knowledge.
Teacher: Please keep your eyes open and carefully observe these pictures on the big screen to see what you findTeacher: This girl in the second column of the first row, tell me what you have discovered.
Teacher: This classmate said that she found that Sun Wukong's golden hoop stick is constantly changing, from the initial 0009 meters became the last 9 meters. The teacher found that you were not only very observant, but also very good!
Teacher: Do any other students have discovered anything else?
Teacher: This student in column 5 just now saw that you were observing very seriously, so tell me what you found
Teacher: This discovery of yours is really remarkable!He discovered that when the golden rod changed, the position of the decimal point also changed.
Teacher: What is the relationship between the movement of the decimal point and the length of the golden hoop stick?Teacher: Before discussing this issue, let's take a look at a simple question:
Teacher: The teacher has a little hint for you, you can write down the numbers, observe them carefully, and see what you find
Teacher: Through the heated discussion just now, it can be seen that you have fully expressed your views, so which group is willing to send a representative to talk about the results of your discussion?
Teacher: Let's talk about the third group.
Teacher: They find out the pattern by converting units and exchanging meters into millimeters.
Division: 0009m=9mm,0.09m=90mm,0.9m=900mm,9m=9000mm.As the decimal point moves to the right, the decimal gradually gets larger.
Teacher: Your group is very creative, which is very valuable!
Teacher: Are there any other groups that observe in different ways?Teacher: In the sixth group, you should send a representative to show it.
Teacher: Your group's observation method is also very unique!They say it's 0009m,0.09m,0.9m, 9m is written like this, and when you look at it from top to bottom, you can see that if you move the decimal point one place to the right, the decimal will expand to 10 times, and if you move it two places to the right, the decimal will expand to 100 times.
Teacher: Yes, when we look down from above, we will find that when the decimal point moves to the right, the decimal will change accordingly, and moving one place is equivalent to multiplying the original number by 10, and the decimal will expand to the original 1. Times;Moving two digits is equivalent to multiplying the original number by 100, and the decimal number is expanded to 100 timesMoving three digits is equivalent to multiplying the original number by 1000, and the decimal is expanded to 1000 times.
Teacher: Now we know that when the decimal point is moved to the right, the decimal will become larger, so when the decimal point is moved to the left, it will be smaller.
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Changing by one digit is equivalent to multiplying the original number by 10, and the decimal is expanded to the original 1. Times;Moving two digits is equivalent to multiplying the original number by 100, and the decimal will be expanded to 100 times, and moving three digits is equivalent to multiplying the original number by 1000, and the decimal will be expanded to 1000 times.
Teacher: Now that we know that when the decimal point moves to the right, the decimal becomes larger, so what happens to the decimal when the decimal point moves to the left?Let's discuss it again with each other.
Teacher: I see that everyone has quickly finished the discussion, which group will report on your results?
Teacher: Just now, the students in the fourth group had the most serious and intense discussion, so please send a representative to tell us!
Teacher: Yes, when we look at these numbers from the bottom up, we will find that moving the decimal point one place to the left is equivalent to dividing the original number by 10, and the decimal point will be reduced to the original 1 10, and moving the decimal point to the left by two places is equivalent to dividing the original number by 100, and the decimal point will be reduced to the original 1 100Moving the decimal point to the left by 3 places is equivalent to dividing the original number by 1000, and the decimal is reduced to the original 1 1000.
Teacher: Now we know what kind of relationship the movement of the decimal point has with the length of the golden hoop stick?
Teacher: Yes, when the decimal point is moved to the right and a few digits, the decimal is expanded to the corresponding multiple, and when the decimal point is moved to the left and a few digits, the decimal is reduced to a corresponding fraction.
3. Consolidate Xi.
Teacher: We have learned so much knowledge Xi this class, have you really mastered it?
Teacher: Now that you have mastered everything, do you dare to accept the teacher's challenge?Look at the big screen.
Teacher: Please ask the students to complete the Xi questions on the big screen independently, compare the changes in the numbers, and wait for the teacher to find the students to answer.
Teacher: Tell me about the girl in the fifth row.
Teacher: You have expressed yourself very clearly, so that everyone can understand it as soon as you hear it!Do you have the same answer as hers, students?Teacher: It's all the same, it seems that you have mastered it very well today!
Fourth, the class summary.
Teacher: Then what did you gain today?Who would like to share it with you. Teacher: The boy in the last row, please share it with you!
Teacher: His report was very complete and wonderful, and he was an example for all of us to learn from XiThe classmate said that he knew that once the decimal point changes, it will also cause the decimal size to change.
Teacher: What exactly are the changes that have been caused?
Teacher: Yes, when the decimal point is moved to the right, the decimal will become larger, moving 1 place, expanding by 10 times, moving 2 places, expanding by 100;When the decimal point is moved to the left, the decimal becomes smaller, moving 1 place to the left and the number is reduced to 1 10, and moving 2 places to the left is reduced to 1 100
Teacher: Today, the students shared very well, and it can be seen that everyone is actively participating in our class, and the teacher is very proud of you!
5. Assign homework.
Teacher: The pleasant class is coming to an end, and after the class, students are invited to complete the first and second questions in the Xi exercise booklet.