Teaching goal of dividing a number by decimal j;
1, so that students can master the division calculation rules of divisor as decimal.
2. Improve students' knowledge transfer ability.
3. Cultivate students' good habit of doing problems carefully.
Teaching emphasis: make students master the rules of division calculation with divisor as decimal.
J teaching difficulty: make students master the division calculation rules with divisor as decimal.
Class arrangement: one class
Teaching aid uses: small blackboard
U teaching process:
U introduction:
Review old knowledge
1. How many times has the original number been enlarged by removing the decimal point of the following number? 13.84.670.725
2. The divisor is enlarged by 10 times. How should dividends be changed to keep business unchanged?
4. Enlarge 5.34 times 10 times. How should the decimal point be moved? Enlarge 1000 times?
5. Students fill in the numbers in brackets:
Bonus 15 150 ()
Frequency divider 550500
Q () () 3 What are the rules for students to summarize? (The Essence of Quotient Invariance)
U show the goal: see the teaching goal.
U self-study tips: combine the goal and the knowledge of fractional division learned in the last class, learn independently and master the main points.
U students' autonomous learning: students' autonomous learning and teachers' itinerant guidance.
U students report and check the effect of self-study.
Research example 5
(1) Teacher: What information is in the picture? According to the data analysis, the formula is listed: 7.65÷0.85(2) Q: Think about it, how to calculate the divisor as a decimal? Convert to division in which the divisor is an integer. (3) Q: How to transform? Organize students to discuss in groups, write the discussion opinions on paper, and let a group of students show them on the video display platform, and explain them while showing. After the explanation, I asked the students in the audience, "What do you think of the result of our discussion?" The students in the audience gave suggestions to the students on the stage, which triggered the discussion of the whole class. Let several groups of students go on stage to explain their views.
After discussion, it is concluded that the divisor of 0.85 should be expanded to 100 times to 85, and the dividend of 7.65 should also be expanded to 100 times, so that the quotient remains unchanged. Note: The decimal point of the divisor in the original vertical form is crossed out with the leading 0 and the decimal point of the dividend.
U cooperative discussion:
12.6÷0.28
How to rewrite this problem into division in which the divisor is an integer? Please rewrite it in the way discussed in the previous question. Pay attention to comparison when rewriting. How is this question similar to the last one? What is the difference?
Students rewrite the formula while discussing. After rewriting, they show their rewritten formula on the video display platform by name. Compare two problems, that is, the division of divisor and decimal, and their similarity. The difference is that the divisor and divisor in the previous question have the same decimal places, while the divisor in this question has three decimal places, while the dividend has only two decimal places.
Teacher: How to deal with the problem that the divisor and divisor have different decimal places?
Guide the students to say that after adding 0 to the decimal point of the dividend, the decimal places of the divisor and dividend are the same, and then expand the divisor and dividend by the same multiple at the same time. Decimal displacement is not enough, add 0 at the end of decimal.
Summary: What did the students learn? The teacher summed it up properly.
U class assignments:
1, do it, page 22.
2. Exercise: Judgment and correction:1.44 ÷1.8 = 81.7 ÷ 2.6 = 4.54.48 ÷ 3.2 =1
3. Exercise: 24 pages of homework in the book.
U class summary: what should I pay attention to when dividing decimal by decimal?
U blackboard writing design: u reflection after class;
The teaching goal of quotient divisor j;
1, so that students can learn to use "rounding" to find the approximate number of decimals according to actual needs.
2. Improve students' ability of comparison, analysis and judgment.
J teaching focus: make students learn to calculate the approximate number of decimals by rounding according to actual needs.
J teaching difficulty: make students learn to calculate the approximate number of decimals by rounding according to actual needs.
Class arrangement: one class
Teaching aid uses: small blackboard
U teaching process:
U introduction:
First, review.
Press "rounding method" to keep the following figures to one decimal place.
3.724. 185.256.037.98
2. According to the rounding method, keep the following figures to two decimal places.
1.4835.3478.7852.864
7.6024.0035.8973.996
After completing the questions 1 and 2, ask the students to explain why the "0" after the decimal point cannot be removed.
U show the goal: see the teaching goal.
U self-study skills: combine the goal and the decimal multiplication approximation knowledge you have learned, learn independently and master the main points.
U students' autonomous learning: students' autonomous learning and teachers' itinerant guidance.
U students report and check the effect of self-study.
Teaching examples of study 6.
For example 6, the teacher asked to calculate according to the information presented in the book. When students divide the quotient by two decimal places, they can't divide it. The teacher asked, "when actually calculating the amount of money, it is generally only' points', so how many decimal places should be kept?" What should I do when I divide it? (Student: To keep two decimal places, only calculate three decimal places, and then omit the mantissa after the percentile by rounding. )
The teacher asked: how much should it be equal to keeping one decimal place? Represents the calculation of "angle".
Teachers should make students think: "How to find the approximate value of quotient?" (first of all, it depends on the requirements of the topic, and several decimal places should be reserved; Secondly, when calculating the quotient, divide it by one bit more than the decimal places that need to be kept, and then "round off". )
U cooperative discussion:
U class assignments:
Find the approximate value of the following numbers:
3.8 1÷732÷42246.4÷ 13
Homework in the book
U class summary: the reduction method of quotient
U blackboard writing design: u reflection after class;
The quotient j: the teaching goal of practical class j;
1, according to the invariant property of quotient, communicate the division of integer and decimal.
2. Solve practical problems by fractional division.
3. Let students feel the instrumentality of calculation and cultivate their awareness of application.
J teaching focus: communicate the division of integers and decimals according to the invariance of quotient.
J Teaching Difficulties: Using Fractional Division to Solve Practical Problems
Class arrangement: one class
Teaching aid uses: small blackboard
U teaching process:
U introduction:
U show the goal: see the teaching goal.
U self-study tip: complete the exercise independently or cooperate with others.
U students' autonomous learning: students' autonomous learning and teachers' itinerant guidance.
U students report and check the effect of self-study.
First, basic exercises
Observe P25, question 8
Teacher: What did you find? Can you fill in the figures in other columns according to the figures in the first column? And talk about the basis. Students think independently, communicate in groups, and correct in the whole class.
Summary: According to the invariance of quotient, we can convert fractional division into integer division, and generally only need to convert divisor into integer. Show me the problem.
Fill in the quotient of the following questions according to 324÷24= 13.5.
3.24÷24=3.24÷0.24=3.24÷2.4=0.324÷2.4=
Please tell the students what they think.
2. Teacher: Students can calculate fractional division. Let's solve the problems in life. Can showing Question 6 solve the problem?
Students independently complete P25, question 6.
Second, key exercises, P25, question 7
What questions can I ask? Will there be any results?
1, students ask questions and the teacher writes on the blackboard. (There may be: ① How many people are there? (including teachers), * * * How many students are there? ② How much is the fare per person (one way)? (3) How much money should each person bring at least? …)
2. Communicate at the same table first, and then communicate with the whole class.
Teacher's summary: I believe that students can find more math problems in their lives and solve them well!
Third, practice P259 independently. Students answer independently
Fourth, challenge P26 thinking questions
Think independently first, then discuss in groups, and finally report in groups.
U cooperative discussion:
U class assignments:
U class summary: talk about feelings.
U blackboard writing design: u reflection after class;