Teaching objectives:
1, so that students can further master the quantitative relationship of fractional multiplication application problems and learn to apply the meaning of fractional multiplication to solve the two-step application problems of fractional multiplication.
2. Let students learn to collect information, find and ask questions in real life situations, and cultivate students' ability to solve simple practical problems.
3. Let students understand the close relationship between mathematics and daily life, and cultivate a sense of cooperation in the discussion.
Teaching emphasis: Find out the quantity of the unit "1".
Teaching difficulty: analyze the quantitative relationship of two-step application problems of fractional multiplication.
Preparation of teaching AIDS: small blackboard, notes, tutoring plan
Teaching process:
First of all, review the introduction: (tutorial case)
Remarkable: Who is the unit "1"?
(1) The number of boys is 3/4 of that of girls.
(2) Seven eighths of the number of willows is exactly the number of pine trees.
(3) A road has been repaired by 2/5.
Two thirds of the students in Class One, Grade Five are boys.
Second, the situation into, stimulate interest (Board paste)
Teacher: The corn needed to install a green sandbag is 3/4 of that of a red sandbag and 7/9 of that of a yellow sandbag. See who can find the unit "1".
The teacher continued to post that "it takes 60 grams of corn to install a red sandbag". According to this information, what math questions can you ask? Students answer the teacher's blackboard writing:
① How much corn does it take to install green sandbags?
(2) How much corn does it take to install yellow sandbags?
③ How many Jin of corn does the red sandbag use more than the green sandbag? (or how much less green is than red? )
(4) How many catties of corn does the yellow sandbag use less than the red sandbag? (Still not as red as Huang Duoduo? )
⑤ How many grams of corn do three sandbags use?
The first two questions are on the blackboard in the middle, and the other questions are on the blackboard. )
Teacher: In this class, let's solve the first two problems first, and put the others in the problem bag for interested students to solve after this class.
Third, cooperate in exploration and explore new knowledge.
1. Who can say, "How much corn does it take to install green sandbags?" How to solve this problem?
The answer on the blackboard: 60× 3/4 = 45 (g)
Teacher: Why use 60×3/4?
Summary: We learned how to calculate the fraction of a number by multiplication (blackboard writing). Calculating the weight of green sandbags is to calculate 3/4 of red sandbags, which is to calculate 3/4 of 60, so we use 60×3/4.
2. (Erase the first question) Teacher: If this question directly asks how much corn is needed to install yellow sandbags? How to analyze this problem? Ask the students to analyze and solve this problem in groups according to the tips in the second tutorial.
3. Communicate and report, read the line chart in the book, compare, supplement and improve your own line chart.
Student exchange teacher supplementary guidance: How much corn does Huangshabao need? Who must know to find out? (Green sandbag), which means you have to find the green sandbag first, and finding the green sandbag is equivalent to finding 3/4 of the red sandbag. How many grams of corn is needed to find the yellow sandbag, which is 7/9 of that of the green sandbag.
4. So, how much corn does Huangshabao need? Can you list the formulas? Who would say?
The answer on the blackboard: 60×3/4×7/9
Teacher: You see, this problem is actually to find the score of a number continuously and calculate it by multiplication (blackboard writing: continuous).
5. Exercise: Please see article 3 of the tutorial: Did I do it right? Please help me correct my mistakes.
(1) Why do you use 72×5/8× 1/3 in the first question? To ask Xiao Ming's age, you have to ask his father first. His father is 5/8 of his grandfather's, and Xiao Ming is his father's 1/3, even what is his 5/8 1/3, so we use 72×5/8× 1/3.
(2) What happened to the second title? The dance team is 3/5 of the chorus, which means what is 5/6 of 60, so it should be 60×3/5. Note the unit "1".
How about 6.60×3/4×7/9? Please look at the tip of item 5 of the "Guidance Case" and try to calculate it. (draw a blackboard)
Communicate and show students' practices, compare which method is better, and what problems should be paid attention to in calculation?
The teacher stressed: when calculating the multiplication of scores, we should simplify the scores first, and then multiply the simplified results. Be careful not to leave out the figures and leave some space between the lines.
Fourth, consolidate the exercise (the fourth item of the tutorial)
Independent answer, collective correction
Five, self-test, hierarchical standards.
The first two levels need all students to do, and the third level needs capable students to complete.
Sixth, the class summary
What are the similarities and differences between the two-step application problem of fractional multiplication and the one-step application problem learned in the last lesson? What is the key to solve this kind of application problem? How to judge the calculation method?
After the students discussed, the teacher concluded: What I learned today is the application problem of finding the score of a number continuously. The key to solving this kind of application problem is to correctly judge whose unit "1" is in the first step and "1" in the second step.