Teaching content: Renjiao version of the first book of the fourth grade of the seventh unit of "math broad angle - pancake problem".

Teaching Objectives: 1, in the experience of the specific process of pancake learn how to rationalize the most time-saving, so as to understand the need to do things reasonably. 2、Try to find the most reasonable solution among the various solutions to the problem from the perspective of optimization, and cultivate students' ability to analyze the problem. 3, feel the operation research ideas in the daily life of a wide range of applications, and gradually develop a good habit of reasonable arrangement of time.

Teaching key point: initially cultivate students to form a sense of finding the optimal solution from a variety of options.

Teaching Difficulties: Finding a reasonable and fast pancake program.

Teaching materials analysis: "pancake problem" is a humanist version of the textbook in the first book of the fourth grade, "Mathematical Wide Angle" in the content, mainly through the discussion of pancakes, how to rationally arrange the operation of the most time-saving, so that the students will experience the use of optimization ideas in problem solving. This part of knowledge is relatively abstract and difficult for students to understand. However, since students have had the experience of watching how the pancakes are cooked in their daily lives, I would like to use this familiar situation as an entry point in the teaching of this lesson, and through examples, observation, cooperative discussion and optimization, to help students understand how to cook three pancakes as soon as possible so that everyone can eat the pancakes, as well as to summarize the order of the time spent on cooking. The order in which they are arranged will minimize the total amount of time spent.

The teaching process:

I. Pre-set scenarios, into life. Teachers: students, you like to guess the brain by a sharp turn? Teacher out of a question to test you: boiled an egg with 5 minutes, boiled 5 eggs with how long? Student 1: 25 minutes. It takes 5 minutes to boil one egg one by one, and 25 minutes to boil 5 eggs. Student 2: It only takes 5 minutes to put 5 eggs together in the pot. Teacher: Why would you think of cooking 5 eggs together? 5 eggs together can save time and energy, it seems that as long as we are willing to use our brains, even the small matter of boiling eggs can find an optimal method. There are many similar problems in life, today we will see in the pancake problem, can you find the optimal method? --Board: pancake problem (Design intention: the use of students familiar with the life of the situation to introduce the subject, not only aroused the interest of students, but also closely linked to the theme of the teaching context is concise and effective.)

Two, around the theme, explore new knowledge. 1, interpret the information, understand the pancake rules. Teacher: you see, mom has begun to pancake, you get from the picture of what mathematical information? Sheng: only 2 pancakes can be cooked each time; both sides should be cooked; 3 minutes per side. Teacher: What does it mean to cook only 2 pancakes at a time? (Student: Only a maximum of 2 pancakes can be in the pan at the same time.) Is it OK if I put only 1 pancake in the pan? Teacher: What if I cook both sides? (The front side of a cake should also be cooked, and the back side should also be cooked.) 2、Observation method, explore the optimal way to cook 2 cakes. Teacher: According to the information in the picture, if mom cooks only one pie, how much time is needed at least? Student: 6 minutes. It takes 3 minutes to cook one side first, and then turn it over and cook the other side for 3 minutes, 3 + 3 = 6, so it takes at least 6 minutes to cook 1 pancake. Teacher: If you want to cook 2 pancakes, how many minutes will it take at least? Student 1: It takes 6 minutes to cook 1 pancake and 12 minutes to cook 2 pancakes. Student 2: It takes only 6 minutes to cook 2 cakes. You can cook two pancakes together, first on the front and then on the back. Teacher: Which method do you think is better? Why? (Save time.) Why does it save time? Sheng: Cook 2 cakes at the same time. Teacher Summary: It seems that this is the optimal way to cook two cakes, that is, 2 cakes at the same time. 3, hands-on, explore the optimal way to cook 3 cakes. Teacher: 3 pancakes, at least a few minutes? It seems that we have different ideas, please use your learning a pendulum, try how to cook the most time-saving. (1) Students try to cook pancakes. (Teacher visits and gives individual instructions.) (2) Reporting. (Expected to have 18 minutes, 12 minutes, 9 minutes) Preset:

① one by one cooking: cooking one to be: 3 + 3 = 6 (minutes) branding three to be: 6 × 3 = 18 (minutes) ② two at the same time, and then individually branded the third: at the same time, cooking two 6 minutes, cooking a 6 minutes, 6 + 6 = 12 (minutes) Teacher: it proved their guess: cooking three pancakes takes 12 minutes, compared to one by one. It proved its guess that it takes 12 minutes to cook 3 pancakes, which saves time compared to cooking them one by one. （Why? (2 pancakes at the same time for the first time.) Teacher: Who else did the same thing? Teacher: Who else is doing the same thing? (③) Pancake 1 and pancake 2 are cooked first on the front side, then the reverse side of pancake 1 and the front side of pancake 3, and finally the reverse side of pancake 2 and pancake 3 are cooked. 3 times, i.e., 3+3+3=9 minutes (Please ask students to come up to the demonstration. (Please ask a student to demonstrate, while demonstrating the teacher's side of the board) (3) table cooperation, once again pose a pose, experience "9 minutes of branding". (4) Collective exchange, compare and choose the best. Teacher: Both are cooking 3 pancakes, why the second method than the first can save 3 minutes? Sheng: There are always 2 cakes in the pan in this method, while sometimes there is only 1 cake in the pan in other methods. Conclusion: It seems that the optimal way to cook 3 pancakes is the same as the optimal way to cook 2 pancakes, which is to make sure that there are always 2 pancakes in the pan, so that the time spent is minimized. Do you want to give this method a name? By changing the order of the pancakes, we ensure that there are 2 pancakes in the pan at a time, which minimizes the amount of time it takes to cook 3 pancakes, which is the optimal way to cook 3 pancakes, and we call it the "alternate cooking method".

Board: alternate cooking method.

(Design intention: the optimal way to cook 3 pancakes is the key to solving the pancake problem. I let the students demonstrate the process of cooking pancakes, students through hands-on operation, explore and try, and then compare, not only can effectively help students to clear their minds, laying a foundation for later learning, but also cultivate the students' creative ability.) 4、Summarize the method, explore the law