course content

Compulsory Education Curriculum Standard Experimental Textbook (West Normal University Edition) Page10/4 Grade Example 2, Class Activities and Exercises 19 Questions 5-8.

Teaching objectives

1. Master the estimation method of dividing three digits by two digits, and be proficient in correlation estimation.

2. Master the estimation method of double digits in trial practice. Grasp the specific quantitative relationship in solving practical problems.

3. Learn to look at life phenomena from the perspective of mathematics when solving problems, gain a successful experience in the process of exploring algorithms, and improve your understanding of mathematics.

Prepare teaching AIDS and learning tools

Theme pictures, video display stands, etc.

teaching process

First, create scenarios and review knowledge.

1. Oral calculation: 80 ÷ 490 ÷ 30800 ÷ 20120 ÷ 4540 ÷ 903200 ÷ 802.

2. Find the approximate values of the following figures. 2386672 1 (mantissa after thousands and hundreds is omitted)

3. Estimation: 79 ÷ 459× 42183 ÷ 6310×194.

Question: How to estimate the division of divisor into single digits?

Teacher: Today we will continue to discuss the estimator.

(Blackboard: Estimator)

[Comment: Make full use of students' existing estimation experience and do a good job of knowledge incubation; At the same time, do a good job of dispersing the knowledge and difficulties in this lesson. ]

Second, independent attempt and cooperative research.

1. Example 2 Theme map: Starting from Chongqing, an ordinary passenger ship can travel 20km per hour and 207km at about (). Make an oral statement and answer it. Tell me how you estimate it.

Key points: 207km is regarded as 200km, and 200÷20= 10 (hour).

2. Give the first set of information in Example 2. Ask questions and talk clearly about conditions and problems.

The total length from Chongqing to the Three Gorges Dam is 624 kilometers. If an ordinary passenger ship travels 23 kilometers per hour, how long will it take to reach the Three Gorges Dam?

(1) and then say, why use division? Key point: some of the 624 will take several hours at 23 (paving the way for summarizing the quantitative relationship "distance-speed = time").

(2) How do you estimate it? Key point: You can think of 624 as 600, 23 as 20, and then do the math orally. You can also think of 624 as 620, 23 as 20, and then do the math orally. Arrange and write on the blackboard according to the students' answers. 624÷23≈30 (hours) 624 23 ≈ 31(hours) 600 20 = 30620 20 = 31

3. Try to practice independently. Example 2 The second set of information.

The total length from the Three Gorges Dam to Chongqing is 624 kilometers. How long will it take to get back to Chongqing if you travel 52 kilometers per hour by high-speed express?

(1) and estimate.

(2) How do you estimate it? If some students can't, you can ask your deskmate, classmates or teachers.

(3) Collective communication-divided into two aspects.

First, why use division? How much will 52 out of 624 take? )

Second, how do you estimate it? (Take 624 as 600, 52 as 50, and then calculate orally) 624÷52≈ 12 (when) 600 50 =12.

[Comment: Let students learn to transfer their ability in guessing, reach a sense of identity with guessing ability in communication with classmates, and gradually transition from concrete to abstract in constant observation and communication. In the process of knowledge formation, students gradually become rational in thinking and estimating knowledge. ]

Third, summarize the popularization and completion of blackboard writing.

Summary: (1) How to estimate the division with a divisor of two digits? The divisor is regarded as an integer hundred (or a hundred dozen), and the divisor is regarded as an integer ten, and then it is divided.

(2) What quantitative relationship have you found from solving the above problems? Distance/speed = time.

Fourth, practice consolidation and skilled estimation.

1. 102.

(1) 180÷90=2 (when) Why is this presentation? Distance/speed = time.

(2) What quantitative relationship can be found when 581÷ 7 = 83 (km)? Distance/time = speed.

(3) How to estimate 762 ÷ 75 ≈ 10 (hour)?

2. Page 103 of the textbook, questions 5-8.

(This case is provided by Huang)