(a) Let students learn to subtract two numbers from one number in succession. That is, to find the surplus twice.

(B) initially cultivate students' ability to analyze and answer application questions.

(C) Through teaching, initially cultivate students' good habits of positive thinking.

Teaching emphases and difficulties

Key points: analyze the quantitative relationship of application questions and learn the first method.

Difficulties: correctly analyze the quantitative relationship and understand the meaning of each step.

Teaching AIDS and learning tools

Write a small flip blackboard with review preparation.

Teaching process design

Review preparation

Oral calculation of the following application questions (it is required to state the quantitative relationship first and then list the formulas)

1. How many classes are there on four Mondays, five days a week?

2.4 The students drew 24 pictures. How many pictures did each student draw on average?

3. A story book is 96 pages, and I have read 18 pages. How many pages are left?

There are 30 colored papers in the school. Made paper flowers 1 1. How much is left?

After the students answered, the teacher added a condition to the fourth question, "It takes 9 yuan to make a small flag". This question is what we are going to learn in this class.

Learn a new course

1. Show examples. There are 30 colored papers in the school, 1 1 to make paper flowers and 9 to make flags. How much is left?

2. Introduction to questions

After the example is presented, let the students read the question silently and understand the meaning of the question. Then the teacher asked a question: "This question is different from the previous application problem. How to answer? " The teacher's doubts arouse the students' positive thinking. At this time, the teacher can guide the students to try to analyze the solution. According to the students' analysis, the teacher also uses a line chart to express the quantitative relationship. Draw a line segment and analyze it.

(1) How many paper flowers are left? (30- 1 1 = 19 (Zhang))

(2) How many cards are left? (19-9 = 10 (Zhang))

Then the teacher asked: what is the first? What is it? At the same time, the meaning of each formula is written on the formula. And ask the students to personally point out which paragraph "30- 1 1 = 19" was removed from and which paragraph was left. From which paragraph was "19-9 = 10" removed, and which paragraph remains. Let the students talk more about their ideas.

Give it a try and then do it.

The teacher shows a problem similar to the example and asks the students to try to finish it independently. Draw a solution idea according to the diagram first, and then solve it separately.

The kindergarten bought 30 apples, 9 in the middle class and 9 in the small class 12. How many apples are there?

Draw a solution first:

Recursive calculation:

30- 12 = 18 (piece)

18-9 = 9 (piece)

A: There are nine more.

Let's talk about which step to calculate first, which step to calculate again, and the meaning of each step formula.

Step 4 do it and think about it

The teacher shows the following two questions, so that students can think independently, solve them first, and then think about the math problems they learned today, which are important first and which are important later.

(1) The store delivered 35 baskets of apples, and sold 10 baskets in the morning and1/0 baskets in the afternoon. How many baskets are left?

There are 24 ducks by the river. Seven ducks swim first, and then nine ducks swim. How many ducks are left?

5. Summarize the problem-solving ideas

On the basis of studying the above four questions, teachers can guide students to sum up ideas to solve such problems. Ask the students to discuss what they know and what they want. (Ask students to answer specific questions) Let students discuss what to calculate first and then what to calculate, and let students try to analyze with comprehensive thinking in combination with specific questions. For example, in the first question (1) of "think before you do it", students can analyze their thinking in this way: the store shipped 35 baskets of apples and sold 10 baskets in the morning. These two conditions can be used to calculate the number of baskets left after selling in the morning, and then subtract the two conditions of selling in the afternoon 1 1 basket from the remaining number of baskets.

In this way, under the guidance of the teacher, let students talk about the problem-solving ideas of each problem in combination with specific problems, which will make students realize the problem-solving ideas of this kind of problems and learn the problem-solving methods.

(3) Integrated feedback

1. the first group of questions: the teacher projects pictures and asks the students to look at the pictures and point out the problems. Xiaoming has 35 books at home, lent them to Xiaolan 10, and lent them to Xiaohong. How many books are left?

(1) Borrow Xiaolan 10 and extract the rest.

(2) Lend Xiaohong five more books and then draw the rest.

2. The second group of questions: column calculation, which requires the whole class to complete with a pen.

(1) There are 64 boxes of chalk in the school, 8 boxes in grade six and 10 boxes in grade five. How many boxes are left?

& gt There are 85 toys in the shop. I sold 26 toys on the first day and 18 toys on the second day. How many toys are left?

3. The third group of questions: calculation and comparison, please answer them.

(1) There are 45 ducks playing in the pond, and 8 ducks swim ashore. How many ducks are left in the pond?

There are 45 ducks playing in the pond. Eight ducks swam ashore first, and then 14 ducks swam ashore. How many ducks are there in the pond?

There are 45 ducks playing in the pond. Eight ducks swam ashore first, and then six ducks swam down from the shore. How many ducks are there in the pond?

Description of classroom teaching design

This part of the textbook is mainly to subtract two numbers from one number and teach students to solve it in different ways. This not only helps to cultivate students' ability to analyze and solve practical problems, but also initially cultivates students' flexibility of thinking.

This part of the textbook has three classes. The first lesson teaches the first solution, that is, one number subtracts two numbers continuously.

By adopting teaching levels such as bringing forth the old and bringing forth the new, introducing doubts, trying to discuss, summing up ideas and consolidating feedback, students can gradually realize their own ideas and learn how to solve problems in every teaching activity. In the teaching process, we also pay attention to drawing line segments to help students understand the quantitative relationship, which not only disperses the difficulties (enables students to find out the intermediate problems quickly according to intuition), but also cultivates students' observation and analysis ability.

blackboard-writing design

Application of two-step calculation method (3)