Second, the story import

Hello, teacher.

Teacher, today the teacher brought a good story to everyone. do you want to hear it ?

Live and think.

Teacher, listen and think back. What's the name of this story?

, play the courseware "Cao Chong Elephant"

Teacher, have you thought of it? What's the name of this story? Say it together.

Born together, Cao Chong is an elephant.

Teacher, who can tell me how Cao Chong is called an elephant? You say, this boy,

Born in 1, he first put the water in the boat and let it float on the water. Then he drew the one with the highest water point on the boat, marked it there, and put the stone in the boat until it sank to the mark.

Then, weigh the stone again and you will know how heavy the elephant is.

Teacher, you know the weight of the elephant when you weigh the stone, right? Then why did Cao Chong know the weight of the elephant when he weighed the stone? Tell me about that girl.

Born 1, because put the elephant in the boat and mark it, then put the boat into the water. As long as you put as many stones, it will be as heavy as the elephant.

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Teacher, how well you speak. Because at that time, there was no scale that big enough to weigh elephants directly.

Answer all the students, no.

Teacher, so I used the weight of the stone instead of the weight of the elephant. Then, if you weigh the stone, you will know the weight of the elephant. Students probably don't know. In the story of Cao Chong elephant, there is also a very important mathematical idea, which is called equivalent replacement.

Teacher, do you want to solve some problems in this way?

Third, explore new knowledge.

First, the initial test.

Display diagram 1,

One big watermelon-four watermelons weighing one kilogram.

Teacher, what do you know?

Raw watermelon weighs 4 kilograms.

Show me picture 2.

Four apples on the left and one kilogram on the right.

Teacher, what do you know?

Healthy, four apples are exactly one kilogram.

Teacher, may I ask a question?

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confused

The teacher has a question, "A few apples are as heavy as a watermelon." Teacher, can you answer Xiaohong's question? Are you confused?

Instructed by the teacher, put a watermelon on the left and a few apples on the right.

Raw 1, put 16 apples.

Teacher, who can say something?

Health 2 theory

Teacher, what we have learned in this class is equivalent substitution, writing on the blackboard, reading,

Through substitution, courseware demonstration,

(2) do it.

1, open the book 109,

Figure 1 one pig = two sheep

Figure 2 A cow = four piglets

Figure 3 Two cows =, sheep

Solve by living

Teacher, how should I change it?

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2、

1 Duck and 1 Goose are playing on the seesaw.

Two ducks on the left, a goose on the right, balanced, three ducks and four chickens, heavier,

Teacher, who is heavier, 1 chicken or 1 duck? Let's discuss it.

3. Look at the picture and answer the questions

Six carrots for two radishes and nine radishes for three Chinese cabbages. 6 Dabai

How many carrots do you want to eat? ,

Students think independently

Life is difficult,

The teacher helps to analyze, use the form of pictures, and then let the students think, the students still have difficulties,

Health 1, 6/2=3 3*9=27

Refer to student 1 to demonstrate, but the students below still look blank.

Teacher, do you have any different ideas?

Third, the topic changes face

1, find the numbers represented by triangles and squares.

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Triangle+Square =240

Triangle = Square+Square+Square Triangle = Square =

Born 1, you can change a triangle into three squares, then divide 240 by 4 and so on.

60 and find squares and triangles.

Health 2,

The teacher tells

2. Find the number triangle represented by circle and triangle+triangle+circle =30.

Circle = triangle+triangle+triangle

Triangle = circle =

Do it while doing it, and then discuss it with teachers and students.

3. Circle+square =9 1 triangle+square =63 triangle+circle =46.

Circle = triangle = square =

Students answer, teachers and students analyze

Fourth, I dare to challenge difficult problems.

I'm at a loss. It's time to finish class.

Teacher, there are still some questions for you to take back and do.