Teaching objectives

1. Understand that the operation order of decimal mixed operation is the same as that of integer, and will calculate decimal mixed operation four times (mainly in two steps, no more than three steps).

2. Use decimal addition, subtraction, multiplication and division to solve practical problems in daily life and cultivate application consciousness.

3. Cultivate students' good habit of discussing mathematical problems and their ability to synthesize problems.

Teaching focus

Master the arithmetic of decimal elementary arithmetic, and be able to do decimal elementary arithmetic.

Teaching difficulties

Understand the relationship between operations by solving specific problems.

teaching process

First, situational introduction

Teacher: A few days ago, the fifth-grade students made a survey on the domestic garbage we usually produce. The following is a survey report of two classes in Grade Five. Teacher: What mathematical information did you get from this survey report?

Student: Grade 5 1 class. Data: A person can produce 30.8kg of domestic garbage around him. Report from Class Two, Grade Five: A residential area produces 3.5 tons of domestic garbage from Monday to Friday, and produces 1.3 tons of domestic garbage every day on weekends.

Teacher: What math questions can I ask after seeing this math information? Guide students to ask different math questions according to different information.

Second, explore new knowledge.

1. Learn the mixed operation of division, multiplication and division.

According to the different questions raised by students, the teacher asked questions selectively: A person can produce 30.8 kilograms of domestic garbage around him, so how many kilograms of domestic garbage does a person produce on average every day?

After the students read the topic, the teacher asked, "To find out how many kilograms of domestic garbage a person produces every day, what books do you need?" Is it given directly in the title? What method is used to calculate? "After students think and calculate independently, they exchange ideas in groups.

Group report, methods that students may propose.

One method: first calculate 4×7=28, then calculate how many days there are in a week, and then use 30.8÷28 to calculate how much garbage is generated on average.

Another method: first calculate how many kilograms of garbage are produced every week, then use 30.8÷4=7.7, and then use 7.7÷7 to calculate how many kilograms of garbage are produced on average every day.

2. Learn the mixed operation of division and addition.

Question 2: A residential area produces 3.5 tons of domestic garbage from Monday to Friday, and it produces 1.3 tons of domestic garbage every day on weekends. How many tons of domestic garbage does this community handle every day on weekends than usual?

Students finish independently, and the teacher should guide the students who list the step-by-step formulas to try to list the comprehensive formulas and calculate the results according to the quantitative relationship between them.

Step 3 summarize the rules

Guide the students to the three comprehensive formulas in the two questions, and draw a conclusion again: the order of decimal elementary arithmetic is the same as that of integer elementary arithmetic, and the law of integer operation is also applicable to decimal operation.

Third, consolidate the practice.

Complete the calculation on page 17 of the textbook.