Article 1 Teaching objectives:
1, estimate the range of the product of three digits multiplied by two digits.
2, column vertical calculation of three digits multiplied by two digits (difficult)
Teaching process:
1, vertically calculate 39× 12 (review and summarize the multiplication of two digits)
2, satellite running animation import
3, blackboard writing topic
4, clear teaching objectives
5. Question 1: Dongfanghong 1 It takes 1 14 minutes for a satellite to orbit the earth twice.
How long will it take? (Review the multiplication of three digits and one digit)
Question 2: Dongfanghong 1 takes 1 14 minutes to orbit the earth, and it takes 2/kloc-0 times for a satellite to orbit the earth.
How long will it take? Put forward the multiplication of three digits and two digits to ask questions and stimulate students' interest in learning.
Complete tutorial question 1 (estimated)
6. Students learn the contents on page 30 of the textbook by themselves, and complete questions 2 and requirements of the tutorial.
(1) Time: 5 minutes;
(2) Students learn independently and complete independently;
7. Analyze and answer question 2, and pay attention to the summary; Focus on question 2.
Question 3: Through the vertical calculation of 1 14×2 1, summarize "how to multiply three digits by two digits" (key and difficult points).
8. Games (Exercise 3 of presenting textbook 3 1 page in the form of games)
9. Summary: What did you learn in this class?
10, layered operation
[1] (required) textbook page 365438 +0 1 and 2;
[2] (Choose questions) Please use the knowledge learned in this lesson to ask the teacher questions.
Chapter II Teaching Objectives:
1, which can estimate the range of the product of two-digit or three-digit multiplication according to the specific situation.
2. Explore the calculation method of two-digit and three-digit multiplication, and calculate correctly.
3. Stimulate students' interest in learning to multiply two or three numbers, and establish students' confidence in calculation.
Teaching focus:
Calculate three digits multiplied by two digits vertically.
Teaching difficulties:
The calculation method with zero in the middle of the factor and the calculation that needs to deal with continuous carry.
Teaching process:
First, create situations and introduce topics.
Students, today the teacher is going to teach you something you have never touched-artificial earth satellite. Do you know its purpose? Without satellite, we can't make phone calls, watch satellite TV or GPS positioning. The convenience it brings to mankind is immeasurable. So today we will learn something about artificial earth satellites-satellite running time. (blackboard writing: satellite running time)
Teacher: (showing the time of the satellite orbiting the earth) Please read this sentence on the blackboard and write down the obtained mathematical information.
The teaching of design intent calculation stems from the needs of life. I create problem situations related to life to stimulate students' interest.
Second, cooperative inquiry to acquire new knowledge.
Teacher: Now we all know that it takes 1 14 minutes for a satellite to orbit the earth. What about two laps? What about five laps? Can you tell the teacher as soon as possible?
Teacher: It seems that all the students in the third grade are good at multiplication. I also know that two laps and five laps won't be hard for you. So suppose the artificial earth satellite orbits the earth 10, will you? (Please stand up and answer)
Teacher: Students, we haven't learned the multiplication of two digits by three digits. It's great that xxx can now do a multiplication of two digits by three digits.
Teacher: Since this simple formula of multiplying two digits by three digits doesn't bother you, let's have a difficult one. (Multimedia display problem) How long does it take for a satellite to orbit the earth 2 1? Who can make a statement? (1 14×2 1=) Can you estimate the approximate product of this formula?
(default is 1) I regard 1 14 as10, and 2 1 as 20,110× 20 = 22000.
(preset 2) I regard 1 14 as 100, 2 1 as 20, 100× 20 = 2000, so1/kloc-4× 20 = 2000.
Teacher: From the students' estimated answers, we know that estimation is the answer obtained by rounding one or two factors appropriately. So who will estimate the answer closest to the exact value? Students, try to calculate. (group discussion)
The design intention is to combine the specific situation, so that students can develop the habit of estimating first and then calculating. Return the class to the students, work in groups, and explore the calculation method of multiplying two digits by three digits independently.
Third, feedback method, optimization algorithm
Teacher: The teacher walked around, found various methods and summarized three algorithms for everyone to see.
Count 20 laps first: 1 14×20=2280 (minutes) 1 14×2 1.
Recalculate 1 period:11=114 (minutes) = 1 14×7×3.
Add them together: 2280+ 1 14 = 2394 (minutes) =798×3.
=2394 (minutes)
Students have not yet got a fixed method to calculate the two-digit number multiplied by the three-digit number that they have just touched. In group cooperation, students can pass on their previous knowledge and explore their favorite calculation methods.
Teacher: Smart students tell me in various ways how long it takes for a satellite to orbit the earth. Look at these calculation methods. Which is simpler and faster?
Teacher: The students all chose vertical calculation, so they must pay attention to the alignment of digits when multiplying two digits by three digits vertically.
Designing the vertical calculation of multiplying three digits by two digits is the problem of digit alignment and carry error that students are most likely to make, and this step just reflects the focus of this lesson. At the same time, students can appreciate the advantages of vertical computing.
Fourth, summarize the algorithm and consolidate the training.
(1) Teacher: See if you have learned the vertical form of multiplying two digits by three digits. Try it! (Ask students to act out the textbook P34 "Try it")
135×45408×25
54×3 1247×2 10
(2) Teacher: The students who are performing the board have already done it. Let's see how they do. (Organize students to find out the mistakes of acting students and correct them collectively. )
(c) Teacher: Summarize the mistakes and strengthen the algorithm.
1, when students do vertical calculation with 0 in the middle, it often happens that 0 is multiplied by any number to get any number.
2. When two digits are put in front, students don't know that it is actually easier to put more digits in the vertical column.
3. The carry is easy to forget or the carry from the previous step is added to the next step, indicating that the number is too large when written in place, which confuses the original factors.
Teacher: The students below these mistakes should also appear, so after summing up these problems together, I hope students will be more careful and accurate in their future study.
This design aims at consolidating students' new knowledge. For the formula with a multiplier of 0 in the middle, the treatment of 0 should be emphasized. When calculating a two-digit number multiplied by a three-digit number, we usually write the multiplier with more digits. Collective correction will also reduce students' mistakes, stimulate students' interest in learning the multiplication of two or three digits, and establish students' confidence in calculation.
Teacher: In the final analysis, learning mathematics is to apply numbers to daily life. Now that the students have learned the algorithm of multiplying two digits by three digits today, can you help the teacher solve these problems? (Multimedia Display Problem)
1, a tap that is not closed tightly wastes 1 12 kg of water every day. According to this calculation, how many kilograms of water will be wasted in one month (calculated by 3 1 day)?
2. The Education Bookstore purchased 209 composition books, and the number of scientific and technological books purchased was 32 times that of composition books. How many science and technology books did you buy?
Design intention: After students have learned the vertical calculation of multiplying two digits by three digits, they should also apply what they have learned to their lives. In this link, two application problems are designed to stimulate students' problem-solving ability and make the original single vertical calculation teaching more interesting and life-oriented. It embodies the close relationship between mathematics and life.
Five, the classroom summary, extracurricular consolidation
What have you gained from learning this lesson?
1, estimate the range of the product of three digits multiplied by two digits.
(1) appropriately round off one or two factors.
Take the divisor;
(2) Take the product of approximate number multiplication as the result of estimation.
2, column vertical calculation of three digits by two digits
(1) Multiplies three digits with two digits, and the last digit is aligned with the two digits;
(2) Multiplying the three digits by the number on the ten digits of the two digits to obtain the last digit aligned with the ten digits of the two digits;
(3) Add the numbers multiplied twice.
Homework: Exercise the textbook P34 1 and 2 questions.
Chapter III Teaching Contents:
Satellite running time (textbook pages 33-34) [three digits times two digits]
Teaching objectives:
1. It can estimate the range of the product of two digits and three digits in combination with specific conditions.
2. Explore the calculation method of two-digit and three-digit multiplication, and calculate correctly.
3. Multiplication can be used to solve some practical problems.
Teaching focus:
The method of multiplying three digits by two digits and its simple operation.
Teaching difficulties:
An algorithm for multiplying three digits by two digits.
Teaching tools:
courseware
Teaching process:
First, create situations and ask questions.
1. Courseware demonstrates the launch of the first satellite. It takes 1 14 minutes for the satellite to circle the earth. The teacher then asked: What about the 2 laps, 5 laps, 10 lap? Let students calculate the time needed to stimulate their interest in calculation;
2. Thinking guidance: How long does it take to go around the earth 2 1? The formula is114× 21;
3. Reveal the theme: satellite running time
Second, cooperative inquiry and problem solving
1. Q: How to estimate the result quickly? Will you introduce your good method to everyone?
Exchange and summarize the estimation methods, encourage students with problems in time and improve their self-confidence. )
(The product of 1 14×2 1 is more than 2000 and less than 2500)
Induction and summary: the approximate values of the two multipliers are obtained by "rounding" respectively, and then the approximate values are multiplied, and the product obtained is the estimated result.
2. Use other methods to calculate the guide. (Group discussion, teacher visit, showing students' calculation methods)
① take 2 1 as 20 plus 1② take 2 1 as 7 times 3.
1 14×2 1 1 14×2 1
= 1 14×(20+ 1)= 1 14×(7×3)
= 1 14×20+ 1 14× 1= 1 14×7×3
=2280+ 1 14=798×3
=2394=2394
③ Divide 1 14 into 100, 10, and 4④ Calculate with tables.
1 14×2
=( 100+ 10+4)×2 1
= 100×2 1+ 10×2 1+4×2 1
=2394
3. Take advantage of the trend and mine the vertical algorithm.
I understand that the multiplier is the multiplication of one digit ... 1 14× 2 1.
⑵ Arithmetic: How to align the multiplied numbers?
(3) Guide students to summarize in their own language.
Summary: vertical three digits times two digits. Multiply the three digits with the two digits first, and the last digit is aligned with the two digits. Then multiply the three digits by the number on the ten digits of the two digits, and the last digit is aligned with the ten digits of the two digits. Then, add up the numbers multiplied twice.
Try page 34 of the textbook.
① When the column of 54× 3 12 is vertical, change the position of two multipliers: 3 12×54.
② Calculation method of 408× 25 factor with 0 in the middle.
③ A simple algorithm with 0 at the end of 47× 210 factor.
Third, feedback exercises to enhance understanding
1. Fill in the blanks
(1) Two digits times two digits, and the product may be () digits or () digits.
(2) When another factor is multiplied by the number on the tenth bit of the factor, the last bit of the product should be aligned with the () bit of the factor.
(3) When calculating integer multiplication, if there is a zero at the end of the factor, you can first put the number () in front of the zero, then look at how many () there are at the end of the factor, and add a few zeros at the end of the multiplicand.
How many can I fill in the brackets?
600×()< 120 1200×()