1. Knowledge and skills. Consolidate the calculation method of two-digit multiplication and division. The calculation results can be checked by a calculator.
2. Ability goal: By estimating the size of the product, students can experience the methods to solve key problems. Through observation and comparison, students can better master the methods of division, trial and error and adjustment. The introduction of "lattice algorithm" enables students to further understand the multiplication theory and promote the mastery of calculation methods.
3. Emotional goal: to learn the "lattice algorithm", understand the mathematical achievements of predecessors, and give full play to the educational function of mathematics. By breaking through customs and encouraging evaluation methods, students' interest in mathematics learning can be stimulated and their love for mathematics can be promoted.
Teaching focus:
Calculation methods of two-digit multiplication and two-digit division.
Teaching difficulties:
Trial quotient adjustment method for division of two digits.
Teaching preparation:
Multimedia courseware and calculator.
Teaching process:
First, create a situation, the introduction of teaching
Teacher: Students, there are many difficulties waiting for you to challenge in today's math class. Are you confident to meet the challenge? Please add a star to yourself after each level. Let's compare who has the most stars in the end.
Create scenarios, encourage evaluation and stimulate students' interest in learning.
Second, independent inquiry, review by multiplication and division
[1] Fill in the questions and estimate the answers.
1. Teacher: Let's go through the first level first. As a group, use the four numbers "9, 8, 4 and 3" to form as many questions as possible about "multiplying two digits by two digits".
Communication: 98× 43 98× 34 94× 83 49× 83 93× 48 89× 43 89× 34 94× 38 49× 38 39× 84 39× 48.
Teacher: In the compiled questions, please estimate which questions have less points and which questions have more points. How do you estimate it?
Students estimate that both 38×49 and 39×48 can be estimated as 40×50, which are relatively small. Both 94×83 and 93×84 can be estimated as 90×80, both of which are relatively large.
Summary: As long as the number of the tenth place of the two factors is relatively large, that is, the number of the highest place of the factors is as large as possible, then the product obtained is relatively large. The number of the tenth place of the two factors is relatively small, that is, the smaller the number of the highest place of the factors, the better, so the product obtained is relatively small.
This link guides students to think and understand in an orderly way. The size of the product is mainly determined by the number of the tenth place of the factor.
[2] Review the multiplication calculation method.
Teacher: "93×84" and "94×83", the products of these two formulas are estimated to be the same. So, which formula has a larger product? We compare the exact quantity of products by longitudinal calculation. Then enter the second level to see who can calculate quickly and accurately. Students can calculate by hand: 93×84 94×83 and tell the calculation method. After calculation, it is concluded that the product of 93×84 is relatively large.
If students study well, they can be guided to understand that "when the sum of two numbers remains unchanged, the smaller the difference, the greater the product, and the larger the difference, the smaller the product". It paves the way for the follow-up study "Who has the largest enclosed area".
2. Show "56×734" and let students calculate vertically. After students practice, there may be two different situations as follows.
Blackboard: 56 734 × 734 × 56 Teacher: How do you think to simplify the calculation of vertical arrangement? Why?
3. Choose the second largest questions on page 64 of the textbook, 82×65, 75×650 and 705×65, and let the students practice and check with a calculator. If you do it quickly, you can choose to do the rest of the exercises in the second big question.
Choose various types of exercises, guide students to master flexibly in the calculation process, reduce calculation steps, simplify calculation, and analyze students' error-prone situation in time. At the same time, pay attention to students at different levels, so that every student has a chance to experience success.
[3] Review the calculation method of division. Teacher: Thanks to the efforts of our classmates, we passed Grade Two. Then we will enter the third level.
1. Display: Fill any number of the digital cards 9, 2 and 7 in the □ of "298÷3□" to form a division formula and estimate their quotients respectively. Think about it, what do these manufacturers have in common?
2. Teacher: Why is the name of the enterprise a single digit no matter how many words are filled in? No matter how many words are filled in the □, the divisor 3□ is always greater than the first two digits of the dividend 298, so the quotient is always one digit.
3. Teacher: If you put 7 in □ and work out "298÷37", how will your business be adjusted? If the initial quotient is large, it should be reduced; If the initial quotient is small, it should be improved.
4. Teacher: You have successfully passed the three levels, and now we will continue to cross the fourth level.
Note: Fill in 1, 3, 4 in the box □98÷39, and estimate their quotients. Please calculate it again to see if it is in line with your estimate.
5. Demonstration: Vertical calculation and check 728 ÷ 56 = 4110 ÷ 47 = 6554 ÷ 65 =
Teacher: We can check by the relationship of "quotient × divisor+remainder", either by writing or by using a calculator.
Through seeking, trying and adjusting quotient, students are guided to pay attention to the synthesis of various mathematical knowledge in the calculation process.