Compared with integers, primary school students are less exposed to decimals and have little life experience in this respect. Therefore, it is relatively difficult for them to learn the concept of decimals than integers. In order to reduce the learning difficulty and let students better understand the meaning of decimals, the textbook of People's Education Edition arranges the study of decimals in two grades, and the understanding of decimals in the third grade is only 1 to 2 digits. Decimal calculation only involves the addition and subtraction of one decimal place and two decimal places. In the next semester of grade four, students began to systematically learn the decimal knowledge of two units. This arrangement not only conforms to the knowledge system of mathematics itself (the understanding of decimals is based on the preliminary understanding of fractions, which has been learned in grade three), but also conforms to students' cognitive and psychological characteristics and new teaching concepts. However, due to the preliminary understanding of the arrangement of decimals in grade three, the meaning and nature of decimals and the addition and subtraction of decimals were arranged in grade four. Therefore, it is difficult for teachers in grade three to grasp the depth and difficulty of teaching, which is easy to introduce and extremely difficult to teach. How can we grasp this degree? The author puts forward the following teaching suggestions.
1 Attach importance to the close connection between mathematics and real life. Understand decimals in specific situations
Decimals are relatively unfamiliar to students, but they are closely related to real life and are widely used in real life. Students can often encounter life situations in which decimals are used, and they can often come into contact with some decimals (such as commodity prices in decimal form in yuan). According to the cognitive characteristics and life foundation of primary school students, the teaching materials have changed the way of converting length units as the starting point. On the contrary, students can use the conversion of commodity prices and monetary units that they are most familiar with in their life practice to introduce new courses. Therefore, students can collect information about decimals in life and read them before class, so as to have a perceptual understanding of decimals. In the teaching process, they can create the situation of commodity trading, guide students to know decimals by exchanging commodities and currencies, and realize the value and function of decimals in real life.
2. Pay attention to students' mathematical practice and give full play to students' main role.
The illustration on page 88 of the second volume of the third grade of People's Education Edition draws a corner of a food store and introduces decimals and decimal points from the unit price of food. In order to expand the classroom teaching space, students can be arranged to shop with their parents before class and pay attention to the price of goods. In teaching, students can try to tell the prices of three commodities by looking at the pictures. Students may read a few dollars and cents, or they may read in decimal. Teachers can teach and learn from each other, so that other students can learn decimal reading. Students use their existing experience to tell the thinking process of a few yuan and a few cents according to 5.98 yuan; When the students report that the price of ham sausage is 5.98 yuan, let the students talk about how to read it. What does this mean? The purpose is to make students understand the practical meaning of commodities expressed in decimals. Then, one student tells the price of the commodity, and the rest of the students tell the actual meaning of the commodity price and write down the price of the commodity. Then the teacher guides the students to sum up the practical meaning of decimal in yuan and how to read it. Teachers are only organizers, guides and participants. Based on students' existing knowledge and experience, students can freely speak, write and discuss in groups, and participate in the whole process of learning, which can effectively play the main role of students' independent participation in learning.
3 Use migration to promote knowledge internalization. Help students to establish a preliminary concept of decimals
As we know, decimals are another manifestation of decimals. One decimal place represents a few tenths and two decimals represent a few percent. Students have learned a preliminary understanding of fractions, gained the meaning of decimals in yuan, and learned the length units of meters, decimeters and centimeters. With these foundations, students can easily understand the specific meanings of one decimal place and two decimal places. Teachers can make full use of the teaching of Example L in students' existing textbooks.
(1 Starting from the decimal point, we find the meaning of one decimal point and two decimal points. The number of teachers and students 10 1 minute, that is, 1 minute is one tenth of 1 yuan, that is,1/0 yuan (board) 2 points? How about thirty cents and fifty cents? Then multimedia demonstration: divide the ruler with the length of 1 meter into 10 blocks on average. How long is 1 block? How about three servings? How to express it in meters? Students have 1 angle = 1/0 yuan, 2 angle =2/ 10 yuan, and for1decimeter = ()/() meter = () meter, 3 decimeter = ()/(. We can also use the same teaching method to understand the meaning of two decimal places.
(2) Know what decimal point it is. In teaching, students can report their height as 1 m 30 cm (for example, Wang Dong's height is 1 m 30 cm). And ask the question: only in meters. How to express it? Next, let the students read the book before organizing the discussion. Let's discuss how to divide 1 meter into 100. How much is each book? How to express 30 cm in fractions? How to express it in decimal? Then discuss how to express 1 m 30 cm in decimal. Then show a set of exercises: 2 yuan's score is 3.8, 1.6 cm, 1.25 cm, and let the students express it in decimal; Finally, guide the students to find that the integer of yuan or meter should be written on the left side of the decimal point in yuan or meter, and vice versa.
In the teaching process, teachers should pay great attention to let students participate in observation, analysis and comparison learning activities, such as guiding students to observe the similarities and differences of a group of decimals and classifying them according to their characteristics, and infiltrating the education of mathematical thinking methods, which is conducive to helping students establish the concepts of one decimal place and two decimal places.
4. Let students think about problems from multiple angles, directions and levels, and master the comparison method of one decimal place and two decimal places.
Example 2 in the textbook compares the teaching decimals and gives the scores of four students who participated in the high jump competition, all of which are decimals in meters. Students are required to rank according to these scores. Students generally have the experience of taking part in high jump, and they all know that the greater the decimal number, the better the performance. In teaching, group discussion can be used to let students find a suitable comparison method. Through communication and mutual inspiration, they can draw a variety of comparison methods. One is based on. According to the position of the four grades on the tape measure, teachers can guide students to transfer the method of integer ratio to decimals. In addition, there are several methods suggested by illustrations in textbooks to directly compare the sizes of decimals.
Pay attention to the migration of arithmetic sum algorithm of integer addition and subtraction in decimal addition and subtraction, and guide students to explore simple decimal addition and subtraction.
Because there are many similarities or similarities between decimal and integer in counting method and series rate between adjacent counting units, the arithmetic sum algorithm of integer addition and subtraction is also completely suitable for decimal addition and subtraction. The problem situation created by textbook example 4 is open to some extent. In teaching, first let students look at pictures and ask more questions about decimal addition and subtraction, then make full use of existing cognitive experience to communicate the relationship between integer addition and subtraction and decimal addition and subtraction, and then let students explore independently, try to calculate, draw conclusions and summarize.
(Editor Xu Wang)