Learning guidance objectives:

1, guide students to do some simple operations by multiplication and division and distribution.

2. Cultivate students' awareness and ability to choose algorithms according to specific conditions, and develop the flexibility of thinking.

3. Let students feel the connection between mathematics and real life, and use what they have learned to solve simple practical problems.

Guiding point: You can use the law of multiplication and distribution to do some simple operations.

Difficulties in guiding learning: You can use the law of multiplication and distribution to do some simple operations.

Study Guide

First, review preparation

Show:

1. Oral calculation:

73+27 138× 100

100-64 64× 1

8×9× 125

(4+40)×25

2. Fill in the appropriate number in □.

302=300+□

(300+2)×43=300×□+2×□

2003=2000+□

(2000+3)× 14=2000×□+□×□

Second, new funding.

We have learned multiplication and division, and today we continue to study how to apply multiplication and division to make the calculation simple.

Show me 102× ()

Students fill in a two-digit number at will.

The teacher quickly gave out its score instead of calculating it by hand.

Show:

Calculation 102×43

Group discussion completed.

Students may appear:

( 1)( 100+2)×43

(2) 102×(40+3)

On the basis of comparison, teachers guide students to observe the characteristics of the topic and how to apply multiplication and division method, so that students can clearly multiply two numbers, make one of them closer to the sum of integer ten, integer hundred and integer thousand and a number, and then apply multiplication and division method, which can make the calculation simple.

Small exercise:

(1) in □

300 1×84=□×84+□×84

92×203=92×(200+□)

=92×200+92×□

(2) Calculate 102×24

Display: 9×37+9×63

Students finish their homework independently.

( 1)9×37+9×63

=333+567

=900

(2)9×37+9×63

=9×(37+63)

=9× 100

=900

Find different ways to implement the performance of the board of directors.

Guide students to compare the two methods, and focus on understanding and explaining the second method.

Summary: The structural feature of this kind of questions is that the operation symbols of formulas generally adopt the form of ×,+and ×, that is, the sum of two products.

In two multiplication formulas, there is the same factor, that is, the sum of two numbers multiplied by that number.

The other two different factors are generally two numbers, which can add up to whole ten, whole hundred and whole thousand.

Small training: (80+8)×25

32×(200+3)

35×37+65×37

38×29+38

Discussion: Does this question conform to the structural form of multiplication and division? Can it be converted into the form of multiplication and distribution law? How to apply multiplication and division to simple calculation?

When modifying, explain how to simplify the calculation by using the algorithm.

Guide the students to sum up: when we use multiplication and division, we must carefully examine the questions and observe the characteristics of the formula. Some of them can't be simplified directly, but we can simplify them by changing the questions slightly.

Third, classroom testing.

Teachers and students set questions.

We use what we have just learned to solve problems. You work out a multiplication formula and I work out a multiplication formula, but these two formulas should be combined and simplified by multiplication and division and distribution.

Fourth, class summary.

Students report what they have learned and what they have gained.

What did you learn from this course?

Verb (abbreviation of verb) extracurricular expansion

P38/6—8