Teacher: Have you ever seen pancakes? Do you know how pancakes are baked? Pancakes should be baked on both sides, first front and then back. This pancake problem is one of the famous problems in mathematics, and there are many mathematical problems worth studying! 2) New knowledge research: 1, solving the problem of "even pancakes": 1) Teacher: For example, if you have a pot, you can only bake two cakes at a time. If you want to bake a cake in this pot, it takes 3 minutes to bake one side. How long does it take to bake a cake? Why? The time it takes to bake 1 cake is 3 minutes on the front and 3 minutes on the back: 3+3=6 minutes (health: because one side of a cake is 3 minutes, and both sides are 6 minutes. ) 2) Teacher: What if I want to bake two cakes? How long will it take? Question: Why is it also 6 minutes? It took 6 minutes to bake a cake just now. Why not bake two cakes for 12 minutes now? Should it be 2 * 6 = 12 points? (health: because the two cakes in it are baked at the same time. It took three minutes to bake these two noodles, and it took me another three minutes to turn the cake, so one * * * is six minutes. ) teacher: good. Two cakes in the pot are baking at the same time, so you can bake two noodles at the same time, so it takes six minutes to bake twice. At the same time, pay attention to the explanation when explaining: the pot is always full and there is no waste of resources. . 3) What if you bake four, six or eight cakes? How long will it take? 4) Summary: Look at this set of data. What did you find? That is to say, the number of pancakes is even, and the way to bake even pancakes is: you can bake two pancakes, each pancake takes 6 minutes, and several pancakes take 6 minutes. (Revised blackboard: 6* 1 6*2 6*3 6*4) 5) Guided observation: Teacher: Please observe this set of data carefully. What did you find? Health: The number of cakes is the same as the number of times they are baked. How many times do I bake several cakes? Teacher: Why is this? 6) Q: How many people are there in our class? If we bake 1 cake for everyone in our class with this pot, how long will it take * * *? Can it be expressed in a formula? Why do you think so? 2. Solve the problem of "odd pancakes": 1) Teacher: When the number of pancakes is odd, how to bake them in the fastest time? Next, let's discuss this problem. If you want to bake three cakes now, how are you going to bake this pot? Tell me what you think. (health: burn two first, then one. A * * * takes 12 minutes. ) Teacher: Besides these methods, are there any better methods? (Give students space to explore: What else can you do to make a brand? Which method is more reasonable? 2) Next, let's give it a try, choose the method we like to learn, and see who can come up with a good way to bake these three cakes in the least time. (The least prominent. Group discussion, teacher patrol. 3) Group Report: Who wants to report the results of your group discussion? Every time the teacher puts a piece of paper on the blackboard, the students report the results of the discussion. Teacher: Who knows? Say it again. The teacher wrote it on the blackboard in the form of 1 2 3, with the first positive, the second negative and the third negative. 4) Lead the discussion: What do you think of this method? (health: it saves time and is faster than the previous method. ) teacher: now, students think according to the teacher's blackboard. Why does this method save time than the previous one? Teacher's prompt: When we just baked the third cake, we only baked one pot that could have baked two cakes at a time, which may have wasted time. ) 5) teacher: "bake only one side of a cake, and then put on other cakes to continue baking." Should we give this method a name? " Student: "..." Teacher: "Good! Let's call it the' alternating pancake method' first! What's the difference between this baking method and grouping baking method? Why save time? " If there are two cakes in the pot every time, you won't waste time. 3. Solve "other strange cakes except 1, 3": 1) So if the number of pancakes is 5, 7 or 9 now, how do you plan to finish baking these cakes in the least time? Please choose one of these three situations to practice. The students answered, the teacher wrote on the blackboard: the number of sheets 13579 ... the minute is 69 15 2 127...7) What do you find after observing these data? "When the number of cakes is odd, what is the law of the time required? How to burn more time? Is there any pattern? Let's discuss it. " Teacher: "The student's discovery is very valuable, so why is it required that the number of minutes is equal to the number of cakes multiplied by 3, regardless of whether the number of cakes is even or odd, except for one cake?" "(1 when a cake is baked, part of the pot is empty, but when two or more cakes are baked, the pot will never be empty through reasonable arrangement. So every time you add a cake, the time only increases by 3 minutes. ) teacher: therefore, when we usually solve problems, we must use our brains to find the most scientific and reasonable solution. 3) Basic exercise: 1, copy 5 1 written materials, and copy both sides. If you put at most two copies at a time, how many copies do you think should be made at least? How did you arrange it? 2. Fry up to 3 eggs per pot, 2 minutes for the first side and 1 minute for the second side. How long does it take to fry four eggs? Five or six? 3. Three people came to the delicious restaurant, each ordered two dishes, and there were only two chefs. Assuming that two chefs spend equal time cooking each dish, what order should they do it, and give your reasons? The chef's cooking time is fixed, but the guests' feelings are different. (4) communication between teachers and students, sublimation of thinking. Teacher: What did you learn from this class? In fact, mathematics comes from our lives and also serves our lives. We can find the best solution to many problems in life by using our brains.

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